Smell, seems to be the one least needed, along with taste, they're pretty connected as well, hence the lack of abillity to taste proberbly when you've got a cold or something, if you doubt me, hold your nose while tasting something and see for yourself.
Beeing blind sure would suck, i would hardly be able to do any of teh things i enjoy, this would be the worst of teh options for me
Beeing deaf would prolly come in second worst, cause it woudl be quite a handicap.
touch would prolly be middle wise, it wouldn't be as much a handicap as the above two, cause you'd still be able to do most of what you do now, but theres many things i would really miss, most of them regarding me and my girlfriend.
Taste and smell would hardly handicap me, it would just suck, so i'd go with one of those, and seeing hwo i always controll what i put in my mouth, but can't really controll how my surroudings smell, loosing smell would have some benefits along with teh disadvantages.
Besides, theres not 5 senses, theres a few more, can't remember all of them but sense of equilibrium (balance) thermo-sensitivity, pain (which should be different from touch sense, according to wikipedia) and i think theres 1 or 2 more, can't be botehred to look it up atm.
