Depends.
Do you like to swarm your enemies with hoards of terrifying monster and then shred your enemy with countless swipes of razor sharp talons and scythes?
then maybe tyranids are your kind of Warhammer 40K army.
However tough armies like the space marines will chew through your numbers with powerful ranged weapons and mighty close combat weapons like Deamonhammers and Chainswords.
So really it all comes down to strategy and luck
I think it really depends on how many you have or how much damage they do
Answer It depends on your preferences: When choosing an army consider its tactics/playing style or just if it looks cool. Do you like hordes of aliens? Then collect tyranids. etc.
There is no best and/or worst army in Warhammer 40k. The points system is mostly fair and reflects how these armies should be played. Tau are good at shooting but not so much at close combat, same with Orks and Tyranids, they're not the best at shooting but can eat you up at close combat (most Orks have a BS of 2 I think)
If you are serious about Warhammer 40K you can only play Orks.
Maybe Tyranids? I don't know much about the Lizard men so it's basically a half educated guess
Defineitley 40K.
In warhammer terms TAU is a young yet sophisticated army which includes kroots and fire units. Personally I believe Tau are the best with Eldar in warhammer 40k.
Anything that is close combat oriented & can move up the table quickly.
AnswerTau.
Uh, there isn't a T....If you could post an example that would help. IF it's in the stats it stands for Toughness If it's races it's Tyranids
it is a warhammer 40k peice for the eldar army there fast atack and conciderd the best way to take down a necron monilith!
No, but it always looks a lot better if your army is matching, and your opponent with appreciate it.