Well since you asked what are Ash’s six best from ALL REGIONS and not GENERAL SIX BEST (which is different), things come out a little differently. You have 8 choices to choose from
One would say Charizard is Ash’s best Kanto Pokemon, but I’d argue that PEAKachu (when he’s allowed to fight at full power and be as strong as he should be) is stronger than Charizard or at the very least they’re equals. Pikachu just has better feats of strength than Charizard and most of Ash’s other Pokemon.
- Bringing down a Regice
- Bringing down a Latios who beat Sceptile and Swellow (two of Ash’s best battlers) singlehandily
- Beating Sawyer’s haxed Clawitzer and Aegislash back to back
- Beating two pseudo-legendaries singlehandily in the KL Finals
- Being the only Pokemon on Ash’s Alola team that Tapu Koko deems worthy of fighting it.
Pikachu at full power definitely takes Charizard’s spot on this team.
Orange Islands: Snorlax
It’s debatable if you want to consider the Orange Islands a seperate region (I personally look at it as a part of Kanto rather than it’s own region) Regardless, Ash only caught two Pokemon in the Orange Islands and Snorlax by a mile was the strong Pokemon. Snorlax is often used a reserve for major battles and when it’s used, it NEVER disappoints.
- Snorlax singlehandedly evened up the odds for Ash against Gary
- Consistently takes out 1/3 of a team by itself before going down
- Rather agile for it’s large size
- Excellent durability
- Solo’d a Frontier Brain
Snorlax is easily the stronger of Ash’s two OI Pokemon (Other being Lapras who wasn’t that impressive)
Ash’s Johto Pokemon weren’t that great, infact I’d say it’s one of his weakest teams (2nd weakest maybe if I’m being precise). Out of this bunch the only decent battlers were: Cyndaquil/Quilava, Bayleef, and Heracross. I was tempted to give this spot to Quilava considering it was Ash’s goto guy for most of his Johto gym battles since Heracross didn’t do much in Johto, but in the Sinnoh League, Heracross made up for his lack of battling in Johto by giving one of the best performances of Ash’s Pokemon in that particular league.
Ash had a good team in Hoenn (His 2nd best imo), initially in Hoenn I’d say Swellow was stronger (since Sceptile was still Grovyle at this point) or Grovyle and Swellow were equals. After evolving, then I’d say Sceptile took the mantle of Ash’s strongest Hoenn Pokemon. He gave good showings
- In the Hoenn League (or Hoenn in general)
- Took down Frontier Brain Spencer’s strongest Pokémon Claydol who beat Swellow (Ash’s strongest Bird Pokémon)
- Gave Brandon’s Regirock a good fight (despite Ash not giving commands),
- Sceptile’s Best Feat: being the ONLY Pokemon in the entire Sinnoh region to beat Tobias’s Darkrai in battle). Sceptile has the juice and is universally agreed to be one of Ash’s six strongest Pokemon in general.
Was the star of DP with 3/4 of the series being all about Infernape where it HAD to look good no matter what even at the expense of other Pokemon. Regardless, even as a Chimchar, Infernape was handling business and ultimately has one of the best battle records of Ash’s Pokemon in general
- 16–5 (or 21–8 if you count his time under Paul’s ownership)
- Beat HALF of Paul’s team in the SL by himself (2 of them while poisoned)
- Consistently beat 2 Pokemon in gym battles before going down or winning for Ash
- Was the only member of Ash’s team (aside from Staraptor) to beat one Paul’s Pokemon during their Lake Acuity battle.
Infernape like Sceptile is universally agreed to be one of Ash’s best.
Unova is one of Ash’s weaker teams with only 3 of his Unovan Pokemon standing out: Pignite, Leaveanny, and Krookodile, but out of those three Krookodile is definitely the strongest, being capabable of
- Bringing down Iris’s Dragonite whoed Charizard as a worthy opponent/rival.
- Krookodile was a late capture, so he didn’t have too many showings, but he was still impressive the short amount of time before the league we saw him battle with him being 1 out 3 Pokemon to score a win in the Unova League (Others being Pikachu and Pignite).
Big fat MEGA DUH! Greninja was EASILY the strongest of the Kalos team whether he’s using his Super Form or his regular form. Greninja to this day is the ONLY Pokemon owned by Ash to ever fight E4 level or even CHAMPION Tier Pokemon on even playing field and gain the upperhand. NONE of Ash’s Pokemon have ever been able to do so.
Base Greninja’s feats
- Singlehandily took a Bisharp that was manhandling Sanpei’s Greninja, Pikachu, and Greninja (before evolving) by itself. After evolving, Greninja was taking it on and winning BY HIMSELF and this BEFORE he active his super form and OHKO’d.
- Instantly KO Sawyer’s haxed Clawitzer who KO’d Noivern (who beat Zapdos) and Hawlucha (One of Ash’s main battlers) by itself back to back.
- Was deemed a worthy opponent by Alain’s Charizard who’s inbetween E4 and Champion level and the two in Base Form are portrayed as equals
- Could fend off Alain’s MEGA Charizard and even overpower it.
- Successfully score a hit on Diantha’s Gardevoir (with tactics admittedly)
- Casually one-shots Non-Mega Pokemon
- Manhandles Mega Evolved Pokemon
- More or less beat Alain’s Mega Charizard in their 2nd battle
- Overwhelmed Diantha’s Base Gardevoir
- Back Diantha’s MEGA Gardevoir into a corner (though Gardevoir was holding back).
Greninja is universally agreed to be one of Ash’s best with strong evidence to suggest he’s Ash’s strongest Pokemon IN GENREAL.
Really, the Alola team is easily Ash’s weakest team to date. Since SM focuses so much on comedy, there’s relatively little action and as a result; Ash’s Pokemon don’t have too many feats of strength to their names. So none of Ash’s Pokemon are really that impressive, not even Pikachu despite being deemed worthy to fight Tapu Koko hasn’t had the impressive showing he did in the past. Regarless out of this bunch, Ash’s strongest Alola Pokemon is Lycanroc, but that doens’t say much since Lycanroc hardly battles and it’s most impressive feat is sweeping 3 Pokemon by itslef, but even then it couldn’t do that without a Sitrus Berry to restore it’s energy. So out of Ash’s Regional Aces, I’d say Lycanroc is the weakest one.
Now for the second question: Could Ash Beat a Champion with this team?
The Anime portrays Elite Four members and Champions are being borderline invincible trainers who could easily swat Ash’s Pokemon as if they were flies. For the most part these guys are at least decent battlers, but they aren’t even close to being Champion level, they aren’t even Elite Four Level. The only Pokemon on this list that has any chance of handling that kind of opponent is either Pikachu or Greninja.
- Pikachu regularly gets beatdown by E4 Pokemon, NOW he MIGHT have a chance against a E4 Ace Pokemon.
- Snorlax definitely isn’t E4 level
- Heracross is weaker than Snorlax
- Sceptile beat a Darkrai, so he may have a chance against NON-Ace E4 Pokemon, but not as good a chance as Pikachu
- Infernape got one-shotted by E4 Flint’s Infernape, so no dice. It could PROBABLY beat a NON-E4 Ace.
- Krookodile is probably as strong as Heracross, so no dice
- Greninja could bate an E4, he could PROBABLY beat a BASE Champion Ace even (Cynthia’s Garchomp, Lance’s Dragonite, Alder’s Bouffalant, Diantha’s BASE Gardevoir or Steven’s BASE Metagross), but he definitely can’t handle a whole team of E4 above Pokemon by himself.
- Lyranroc the weakest here so definitely no.
If this was Ash’s BEST TEAM (take out Heracross, Krookodile, and Lycanroc and insert Charizard) than the result wouldn’t change. Charizard’s strong, but he probably can’t handle E4 Aces either. His chances are as good as Pikachu’s, but Mega E4 Aces are above his payroll.
FP Peakachu (Currently) = High E4 Ace Level
Charizard = High E4 Non-Ace Level (At worst) or Mid E4 Ace Level (At Best)
Snorlax = High Frontier Brain Level
Heracross = Mid-Frontier Brain Level
Sceptile = Low-Mid E4 Non-Ace Level
Infernape = Low-Mid E4 Non-Ace Level
Krookodile = Mid-High Frontier Brain Level
BASE Greninja = Low E4 Ace Level (At best)/ Mid-High E4 Non-Ace Level (At Worst)
ASH-Greninja = Base Champion Ace Level
Lycanroc = Low Frontier Brain