Well, I've never used speed potions myself, because I read they merely last 3 rounds.
So even if you can apply them to 3 characters at the time (by making them stand as close as possible and throwing the potion from a distance right into the middle), thats still not really that much.
At least certainly not for the actually hard battles, anyway. When I actually would want a big boost in the first place.
Haste on the other hand lasts 10 rounds, or as long as you can keep concentration, and with a Sorcerer you can apply it to two people at a time, too.
P.s.: Where rounds means turns. Sorry, sometimes I use the terms of older versions of D&D. In AD&D a turn was 10 rounds, or 10 minutes, while a round was 1 minute.
