Glad you're enjoying it! I recommend starting with Space Marines or Imperial Guard, as they're a bit easier in general to get to grips with. Tyrannids are really fun, but also kinda tricky to do well with, since they lack ranged options and you need to manage Synapse units. This makes particularly the early game kinda rough. Tau are also a very effective faction, just so long as you can keep the nasty dudes with chainswords at a safe and plasma-incinerated distance.