Well that's a pretty broad range of options.

I'll say first that Big 'Uns appear to be one of the better ways for Tyranids to be competitive. That said, you need to really consider some basic list ideas.
Antitank?
- Hive Guard, Zoanthropes, Tyrannofex
Big Melee Units?
-Trygon, Hive Tyrant, Carnifex
Troops?
-Tervigon, Termagants, Genestealers, Hormagaunts
Specialty Units?
-Doom of Malan'tai, Deathleaper, Ymmgarl Genestealers
Fast Units?
-Gargoyles, Genestealers, Shrikes, Harpy, Raveners
HQ?
-Hive Tyrant, Winged Hive Tyrant, Warrior Prime
I would pick some sort of imaginary goal (fast, big, shooty, etc.) and somehow get a look at a Tyranid codex through whatever means you feel necessary, and put a rough list together. Once you have SOMETHING for Dakka to peruse, you'll get some useful advice.