I don't know what your price range is ..... but I borrowed each of these for 2 weeks.....
Studio Projects T3
Rode NTK
MXL V69 Mogami
I was lucky enough to demo them all in my own home. They we're all excellent.
The T3 has all the different polar patterns (cardiod, figure 8, and omni). The V69 was very affordable and sounded good, but I do remember liking the sound of the NTK the best.
I read once, as a general rule of thumb - that it is a good idea to have a tube in the signal chain somewhere, on some instruments - because today's Digital equipment (DAW's) can sound cold and un-forgiving, where as a tube will add harmonic distortion - which could make it easier to mix sources together, as opposed to straight digital recordings.
The same book said to add a tube preamp (like the ART you have) to a solid state mic, or a tube mic to a solid state pre. Either way - you'd be adding some tube color.
I do not know a scenario in which you would not want some "warmth" on a track.
Tubes can, but don't necessarily, add any significant distortion or warmth. Some of the best tube equipment simply comes across as being hifi - Pendulum and Millennia gear for example. I've got both, and while they have their own character, I wouldn't characterize it as being "warm". Generally the most coveted gear for preamp color (sometimes characterized as warmth) is solid state gear like Neve, API or Great River. The "warmth" comes from iron -- the transformers in these preamps. Lots of great music has been recorded with solid state pres (API, Neve) and solid state mics (Neumann U87, Gefell M70, Neumann KM84i) and dynamic mics (SM7, SM57, MD421, etc.) used together. Pro audio tube gear isn't really analogous to a tube guitar amp with its very prominent tube distortion when driven.
In addition, the recent use of "toobs" in lower cost audio equipment has largely been an exercise in marketing hype to get people to buy the stuff. The tubes typically don't operate at proper voltage (sometimes referred to as starved plate designs) and simply add a veneer of distortion to the sound, which while it can sometimes be useful as an effect, isn't the "warmth" that people think they are getting by using a tube preamp. Presonus Blue Tube and the Art Tube MP are examples of this kind of gear. Generally, it costs more to build good tube gear than the solid state equivalent - so if you are working on a small budget, you are typically better off buying a solid state unit than a tube unit for equivalent dollars. About the least expensive real tube preamp currently available is the GT Brick. Some people here have said nice things about the EH gear, but I've never used one. Some people here also like the ART MPA and
ART Prochannel which I believe both operate at proper voltage. After that the price goes up significantly with Sebatron probably being the next step (unless you can find a used Peavey VMP-2 or a GT MP1). This isn't to say that you shouldn't buy any of the starved plate gear - the VTB-1, in particular is a nice cheap high gain pre without the tube circuit engaged. It is just that you need to be aware that the toob hype is just that -- hype.
In microphones, some of the newer tube mics appear to use subminiature mil spec tubes, which work fine, but don't seem to have quite the same character as the larger tubes used in the classic microphone designs (U47, M582). That said, it seems that gear manufacturers have done a better job, IMHO, with lower cost tube mics than with preamps. Marshall, SE and Rode among others seem to put out some very nice stuff for the money. Some of the subminiature stuff out there also seems pretty good, but I find they aren't as obviously "tubey" as a mics sporting a classic preamp tube like a 12-AT7. The sound difference between the older GT MD1a (with a 12 AT7) and the GT-44 (same as the GT Alesis AM-40 and with a subminiature tube) is pretty significant. I have and like both mics a lot, but the MD1a comes across with a thicker tube sound and the GT-44 comes across as more hifi. I have a pair of the TNC ACM-310 tube mics and I think they sound pretty darn good - especially for the price. I'd have no qualms throwing them up on overheads or using them on acoustic guitars in a mix. Are they better than my Josephson C-42s? No, but they cost a small fraction of what the Josephsons cost. I haven't yet compared them to my GT-44s, but I suspect they are pretty close in character.
I guess all I'm trying to say here is that one needs to be careful about believing the generalizations that are often made with respect to tube audio gear. It ain't necessarily so.