Pretty much all these options are viable. Depends where you want your tyrant to be really.
I found after much experimentation that i can trust the forward rush to trygons brought in a little sooner by hive commander, (along with all the rest of the little gribblies), so didnt need the tyrant up there as well. Therefore the tyrant got ranged weapons and does pretty well with them... rarely killing his points, but he's also HQ, serious deterrent for anything coming to the backline, and bringing in reserves faster, so doesnt need to kill his points worth. (By the way, stranglethorn is rather better than heavy venom on him i reckon.)
For melee builds, old adversary + LW/BS+any other weapon (throw a cheap gun like devourers on in case) works really well. Had great fun with a flying melee tyrant - but you need to treat him as a bullet magnet when you're doing that. IF he makes the combat then its great. Most of the time, he'll die on turn 1's shooting.
For me, i'd rather i kept the tyrant alive doing his thing, so i end up with the ranged tyrant of (hive commander, stranglethorn, LW/BS, armored shell)... It rather depends on the rest of your army as to what you go with, much like the rest of the tyranid codex.