HD has several resolutions ranging from 480P (852x480 or there about used mostly for web) to 1080P (1920 x 1080).
frame rates vary from 24P (progressive) 25P 25i(interlaced) 30P 30i (and sadly 29.977) 50P 50i 60P 60i (another decimal frame rate i can't remember to).
the pixel aspect ration is square. as a bonus all the aspect ratios are 16 X 9, so nice and wide (unless you're broadcasting on the beeb in which case 14 X 9, but they'll take 16 X 9)
afx has presets for Hd so you might want to check the exact parameters in the new comp dialogue, 3ds might have some to.
I'd say render progressive 60 and 1920 x 1080 for maximum quality (you can always down rez later) but your render times do have a habit of going through the roof so you might want to try a slightly lower resolution and slower frame rate. you'll have to judge the content yourself.