Well, I have been playing all era with inf and currently have 18 squads of inf. I am joining an alliance that is veh build so should is stick with inf or switch to veh?

switch, keep ur 18 squads of inf for killing small fries.

If its early in the game and you know your gonna have time to build another 18+ sqauds of veh then go ahead. If not then I suggest you stay with your inf and fight alone and only join a big battle if needed.

If you're going to change build I suggest you waste your inf sqauds by going into battles you know you're going to win, this gives your inf sqauds exp to use later maybe and also reduces the overhead so you can build veh cheaper and quicker.

depends on what tick u r like santos said..
but as it is u've already 18 squads i guess too late 2 switch..