I do think that the only thing that really matters is the end result. Program is just a tool.
And to be completely honest- i have yet to see anything made with Sludge, that couldn't be easily done in AGS and vice-versa.
I think those two programs are the most advanced adventure-makers out there and you won't go wrong with either of them.
AGS does have very powerful scripting language (you can script everything from start to finish if you want- it's your decision). I'd really recommend you to download 2ma2's amazing platform-game example made with AGS, for some clever scripting.
Now, it depends what you like about adventure creation- if you like to program (script), i believe Sludge will most likely be better solution (as i heard, it's harder, and so gives to programmer more "satisfaction" when he/she program something succesfully)...
If however you are more interested in design, graphics, etc. part of creation, i'd recommend you AGS.
It's your call.
http://maniac.adventuredevelopers.com/ -home of Ignac