Well, in truth I'm a beginner in most respects so I'm not entirely sure what lists would work but I know I'd eventually like to start building a few armies in 750 point chunks, playing a game or two between to see which style I'd be better suited for. I know myself as a player would like a balance of of hordes and monsters. I like Tyranids because of their classic signature playstyle, lots of gaunts/gants/rippers charging ahead in between Carnifexes, Warriors, Thropes, and Vores with a Tyrant at the lead. And now it seems that Carnifexes, Warriors, Thropes, and even Vores are cheaper than ever points-wise, with entire broods of those guys rather than single miniatures.
More specialized unit combos like Trygons/Mawlocks + Raveners, Crones/Harpies + Gargoyles, Tyrannofex + Exocrine, Toxicrene + Haruspex, will all come at a later time when I actually understand them better. I've never really been good at picking specialized units because I used to fall victim to a superiority complex when it came to my old Terminators and Assault Marines back in the day. :P
Oh, and on the matter of specializing my hive fleet, I do like the methods put forth by Kraken with thousands of smaller tendrils causing havoc and confusion while the main force continues to reinforce the tendrils from the main body. I kind of want to follow a similar theme with my own force.