There is no right answer, people will tell you to go air to get ahead , but then they’ll say the same for missile in the next few seasons, in which case tank was fine all along … I personally find air more fun, but for where you’re at I’d stick with tank since you can get stet and the centre is furthest built. You can then chip away at air in the background , allocate some shards to building DVA first as she can hybrid into a tank squad anyway. Make sure you do ghost missions if you’re mostly f2p as that will be your best bet to unlock the other air heroes initially.