That's a very big question you just asked.

T2 land is arguably where the most diversity in the game is found. MMLs are usually only used to outrange T2 PD (they are the only mobile T2 unit that can do this), but are useful as a general artillery unit too. Cybran have the best MML as their missiles can withstand a hit from TMD (they split into three weaker missiles).
UEF and Cybran T2 bots are long range but relatively weak, protect them with shields (UEF) or stealth (Cybran), and use their range to your advantage by kiting the enemy.
UEF and Cybran amphibious tanks are useful on any map, water or not. The UEF Riptide is especially useful for repelling T1 spam, huge HP and very high rate of fire. Cybran Wagner is front-loaded and hard hitting, but has lower HP. It's quick though so you can dance around enemy units with it.
Sera T2 bots are short range and slow, but they are tougher than anything else in T2 so if they get in range they are massively powerful. If there are Sera T2 bots coming towards you, then you might want to think about upgrading to T3 land to avoid getting ripped to pieces.
Flak is pretty much the same across all factions and is excellent against all T1 & T2 air, and gunships of all tech levels. It is also good against massed T3 air (ASFs or strat bombers) due to its splash damage.
There's plenty more, but that should give you a bit to go on.
