[String7th]

I asked the same question here a while back. I learned that tubes do not always mean better. It's the quality of the preamp.

A Behringer ultragain pro has 2 12ax7 preamp tubes in it and costs $199
An SSL single chanel strip pre does not have tubes and costs $1200.
You can probably guess which one sounds better. Not that price has anything to do with it, but the quality and what you're looking for in a preamp makes the difference. Guitar tube gain and recording preamp gain are not the same thing.

They suggest on the Presonus website that the tube chanels should be used for vocals and as a bass DI for a little overdrive. The non-tube pre's should be used for drum mics and guitar mics. But there's no wrong way to do it. I personally would use the tube pre for a snare mic because it's got that limiter on it.