Of the infinity engine RPGs which ones would pick for the following categories:

Best Character Creation System:

Best Story:

Best Characters:

Best Dialogue:

Best Combat:

Best Quests:

Most Repayable:

Most Openended:

Personal Favorite:

I imagine this will be the general opinion.

Well, considering the Infinity Engine was only used on:
PST
IWD 1 and 2
BG 1 and 2

IWD is generally considered 'meh'.
No one ever talks about IWD2
BG 2 is widely considered better than BG1, and often listed in at least the top five RPGs of all time.
PS:T is a very hit or miss game with people, because it's more like an interactive book than an RPG, so it has a strong focus on characters, story and dialogue.. >.>

There's a few freaks like me who prefer IWD over BG, but.. we're few and far between.

Well, you could definitely make an argument that the IWD games have the best combat. Can we include ToEE despite not playing similarly at all?

Seeing how the limit set by the OP is the game's engine, that wouldn't be a problem... if it used the same engine. It doesn't.

Hmm I've played a little bit of all those games. I guess I'll just have to finish them then come back and post.

I'll be back in a few years...

Pretty much this, but the best combat is definitely in Icewind Dale 2.

Best Character Creation System: Icewind Dale 2

Best Story: Planescape: Torment

Best Characters: Planescape: Torment

Best Dialogue: Planescape: torment

Best Combat: Icewind Dale

Best Quests: Baldur's Gate 2

Most Repayable: Planescape: Torment

Most Openended: Baldur's Gate 2 or Planescape: Torment (openended in different ways)

Personal Favorite: Planescape: Torment

Icewind Dale 2 had better combat than all the other IE games, but really I think that was more of an apology by Black Isle that the game was practically 100% combat. Also IWD2 was the first (and only) IE game to use D&D 3rd edition rules, a pretty half-assed adaptation of them, but more complex compared to the rules system in the other games, IWD2 had a fantastic amount of options for characters once you leveled them.

And all the IE were linear (both in terms of story and landscape progression), Baldur's Gate 1 was probably the least linear due to it's world map being the less restrictive.