The swap is actually pretty easy....imo it's harder to change brakes on the car than it is to do the tranny swap.
1) It's hard to get a tranny for $250 to $350. The ones that come at this price are usually beat up pretty bad and will require a rebuild. A GOOD tranny will run upwards of $1000.
2)You do not have to cut a hole in the floorboard for the shifter. You simple swap out the lower shift boot with the Autoshifter.
3) My walk-through goes over pretty much everything you'll run into. It describes some problems you may encounter. Read it first before seriously considering doing it and see if you have the desire for the work.
4) Two guys working SOLID at it can get this done in a weekend. This is of course assuming you already have all tools, equipment, fluids, parts, and sweat to get it done.
5) The AOD is larger (gurth and length) than the 5-speed...it also weighs more. You will need a different rear-crossmember, which is discussed in the walk-through.
6) Your always gonna get different answers about which is quicker. I swapped to a 5-speed because I find it more fun. I enjoy the thrill of being able to go through a corner, holding it in 3rd gear, and punching it when I come out. With an auto, you can still do similar, but it just doesn't feel the same. Also, most performance drag cars (I'm talk'n full blown alcohol type here) all use a "manual" type tranny.
I can drop my tranny in about 50 minutes now. If you've never done it, I would give about 3 to 4 hours to drop it the first time. (Just to give you an idea).