You have a lot of good tanks already if I remember right, so you're good on those for a bit. So I'd go with some Air tech. First off, I'd build a drop ship, or a troop carrier (I think they're the same, if not... well, I'm still right) as they are the easiest to build (If you have the right parts), or work into a forum battle. Then, maybe a gunship, as they are probably as easy to work into a forum battle as well. So, that's my advice.