I have not used either. Just sayin', but I prefer the Shelmet/Accelgor line just a little bit over the former; maybe because the other one decided to
SHELMET/ACCELGOR
Which has a better design?
Both of lines are great design-wise, but Karrablast was a let-down. At least Shelmet had that snail-in-a-helmet going on. Evolutions, awesome.
SHELMET/ACCELGOR
Which is better in battle?
I have no experience with them, so I'll say they're tied. Most likely because they'll be used for different reasons.
TIED
Which is more helpful?
Again, different roles in battle. Not like they have the ability 'Pickup' or anything, but Accelgor's Hydration could be useful in Rain. Escavalier looks like it's all about itself... THIEF
TIED
Which one is your favorite?
Don't know yet. Leaning towards Accelgor for that little background story, though.
TIED
Who has the better movepool?
Escavalier, it's level-up movepool alone compliments it's 135 Base ATK very well.
KARRABLAST/ESCAVALIER
Who would win in a fight?
Dunno, probably Escavalier. It's DEF and SPDEF block all Mixed Moves from Accelgor, but not the other way around. Escavalier's 135 ATK to Accelgor's 40 DEF? Ouch. That's in-game, though. In the anime, Speed + Dodge plays a huge roll, so it could go either way, but I'll give it to Escavalier.
KARRABLAST/ESCAVALIER
Wow, they're tied. However, I'll input some personal bias and choose Accelgor. I'll most likely be training both anyways. So I'll see if I can forgive like Escavalier a better.