well if's between touch and speed i would actually say touch is possibly a bit tougher to train however speed will take longer to gain (assuming you had a perfect 50:50 ratio between the two in your training)
with speed you simply cannot fast track - the tendons/ligaments/muscles all have to adjust, become more flexible etc to increase speed and there is a limit on how quickly they can adjust...e.g i think it's impossible to have the speed in your legs to do a 3 revolution trick in less than 6-8 months of freestyle (i'd love to be proved wrong here)
with touch, you can train it and gain a good touch on both feet i think within a few months (that is, perfect control/balance of both feet) assuming you were only to train your touch...as for endurance, that's another matter!
Very difficult to compare i think overall, i would say the hardest thing in lowers is to be a perfect allrounder in lowers! (skora, ars, mp, becs) - i mean ability to do long combos, long nt combos, 3 revs, ahm/aht etc!