Best strategy: go rainbow or 3 color level 1 mages on all space you can build on before upgrading uniformly EXCEPT for levels that are blatantly weak to one element. One wave through can and will kill you, so just go rainbow.
Red specialists are horrible. If you want proof, play the paving level with 4 buildable spaces and 5 lives. With red specialists, you lose. With red generalists, you win. Even when you have a group of slow, clumped zombies in one lane, for red specialists to theoretically obliterate. With specialists, you will lose the round.
With generalists, you win.
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