If you got C/C++ background then Sludge can be extreamly powerful in the long run. AGS can be powerful too, but to tell you my opinon, the interface of AGS is EXTREAMLY clutered and a pain in the arse. Sludge is damn near perfect in theinterface department(Except the Z-Buffer editor, godam I hate that thing) Also ease of use is a plus with Sludge, I downloaded sludge about 3 days ago and with a few look ups in the EXTEAMLY compleat Help file I was turning out sample rooms as fast as I could draw backgrounds in Photoshop. (Note I'm still using default sprites and cursers but thats next on the list of things to do and from what I experimented with, its a pretty easy to use Sprite animation editor) You do have to download a text editor called Editplus2 and drop in a file to turn your Sludge code colored but all the instructions on that are on the Sludge main page.
My vote, Sludge.