Playing without medic truck can be risky.
I'm not saying to skip it, I'm saying its not needed before first light armor hits the field. You'd have medic truck by 8-10 min anyway.
An early puma isn't really going to wreak battlefield havoc, I don't know why you would rush it over a flaktrack unless you're expecting an M15 or something.
I like reliability of Puma. I don't have enough attention to keep flak HT alife, so I've decided to not build it over Puma as Puma is pretty great against sov and USF T1 builds.
In other words, there isn't really any reason to get flah HT over puma for me personally.