Best Tube for Classical,,,300b or 45's ??

It depends on your speakers. If the speakers are efficient enough to handle large scale music with 45s, then they are fine. If you are using a subwoofer with a dedicated amp, and just using the SET for lower mids and up, then you have quite a bit more flexibility, but may have sub integration seams.

In general, I'd say if your speakers go much below 40Hz, then the 45s will be getting stressed to the max, even on efficient speakers. The bass frequencies take the most power to reproduce, and the lower you go, the more power you'll need. Using a sub with its own amp can help this out alot. If you're trying to get down to 20Hz with authority, you are going to be having trouble with the 300B also. It only makes about 8 watts, and that doesn't go too far at 20Hz. But they both will do the frequencies over 40Hz quite well on an efficient set of speakers.

The 300B is noted for its "fatter bottom end", and the 45 is noted for its totally awesome tone overall. Compromises are going to be found in all systems, and you have to decide what is the most important to you.

I basically agree with Tom above. Both are very nice tubes.
Some folks prefer one - some the other. More important are the amps' design and the match with the speakers. Classical orchestral music can be challenging (dynamics) and you want a lot of headroom. If you are running a SET (one output tube) you will want at least 100db speakers with a 45. With a 300b you might get by with 93db or something.

I remain,

There really is no particular tube by itself that's better for classical in my view, it really depends on the circuit the tube is used in, and the characteristics of the speaker the amplifier is driving. If you have an amp that can use different types of tubes, such as my old Jadis JA80s (6550s, EL34s, KT88s, KT90s), even then you can't generalize, as all can shine depending on the classical music you like and the sensitivity of your speakers--for example, for smaller scale pieces without deep bass and with vocalists, I might prefer EL34's, which shine in the midrange in that unit but are weaker in the bass; for Brahms, Mahler and Russian full scale pieces, I'd opt for KT88s or, if they're Tung Sols, 6550s, which are stronger in the bass and have additional power for the dynamic demands of that music. I guess it really would all come down to your auditioning of the amp/speaker combination you are interested in to see if it works. However, for large scale orchestral works, you will need plenty of power and bass response; either look at higher-powered amps or very efficient speakers.

300B is the king for most systems and music tastes. Sophia Electric 300B does have some sonic characters of 45 tube. We newly introduced a Globe 45 mesh plate tube, several users commented that has killer bass for a 45 tube and sounded better than vintage 45 tubes with high end horn speakers. Check out more information at www.sophiaelectric.com

Richard