I currently own both a DR-10 (all-bipolar transistors) and CA-300 (mix of J-FETs, MOSFETs, and bi-polar transistors). I like the wide, deep soundstage, pinpoint placement of instruments, and lifelike midrange of the DR-10. On the other hand, to my ears the CA-300 is a little more lively sounding, with better instrumental timbre, better bass authority, but not as wide and deep a soundstage or as pinpoint instrument placement as the DR-10.
I find it hard to pick either one as being better or worse. They're just different and I like both. If forced to, I could live with either one. The CA-300 and CA-400 are similar in performance, just that the latter offers more headroom. I would not agonize over type of solid state device (FET or bipolar).
What are your other system components ? Room Size ? Unless you have highly inefficient/difficult to drive speakers, a large room, and/or like to listen really loud, you may find the CA-300 to be more than adequate.