It depends on the overall sound that you want out of your snare. If you want really crisp tight sound then torque everything really tight both top and bottom snares as well. if you want more of a country sound ease off on the torque on the heads quite a bit and reduce the amount of tension on the snares until you reach warm and fuzzy. Experiment.
on my piccolo snare i tuned the bottom head medium tight and the top head just below medium, with the snares medium tight. i got a really full, deep sound from it. but it was deeper than my main snare so i tuned it back up to a nice crackly pop.
I actually tuned mine to my current setting after reading an interview with Mike Wengren (Disturbed). Both heads are tuned tight... and I do meantight! I like my snare to pop/crack; very explosive. if you want a fat sound loosen the head. not sure exactly how to tune the bottom head tho.
I used to tune the top of my Pearl tin piccolo veeerrrry tight. But if you use hard sticks (like oak) their heads tend to splinter quite fast.
But recently I played the drum kit of a friend of mine and he uses a quite deep Sonor snare.
And I was amazed by the great rebound and the smooth and soft feeling resulting from a medium tuned top head.
Tense tuning sounds great (Ping!) but too much seems to kill a lot of the rebound, the head gets very hard and so the feeling of every stroke. So I'm gonna try to tune my bottom head more upwards and lower the tension of the batter head.
I used to try loose tension and tight tension..etc...After all these years I have come to notice that the drum itself has alot to do with it....Now I just find that tuning up to what makes the snare sing and feel good is pretty much it...I would tune real tight thinking that that's the way it is...ewww choked sounding....Just like toms I think the idea is to tune to the drum and if you don't like it, look for one that will work with the tension you do like...I know that's not easy to do cuz they cost doe and you may need to search for a long time...never the less I'm so much more happy with that concept..the other day for the fun of it I tightened my heads real tight and I lost so much power and tone..I detuned it back and played it live this last weekend..I received so many complements while at the same time loving it....My vidios on my myspace show a lacking of crack on the snare cuz of lack of DBs in the mix but also I tried a real tight bottom head with a medium batter side..It did sound good but lacked crack..The reason is that I was trying to get something different than the drum would sing to...I no longer have that snare..Sold It !! Anyway that's my 2 cents