Good question. Many believe the EL84/6BQ5/7189 to be the best sounding non SET tube. Power is limited to 15-25wpc in most applications however and that can be a problem for some.
I do have experience with this tube and amplifiers using this tube. I have a fully restored Eico HF81 which sounds divine driving Spendor 15ohm LS3/5a speakers.
I am intrigued by the Musical Reference RM-10-II and will investigate it.
I would also look at LEBEN for a new or recent amplifier. My opinion of LEBEN in general is that their equipment is like a tube amp from the golden era that is restored and brought up to date with modern higher quality components but keeping the classic design.
I would look at the following vintage amplifiers:
Fisher 20a and 30a monoblocks. Fisher SA100 stereo amplifier. All 3 are superlative. Deep bass, liquid midrange, and clear extended treble.
Eico HF14 monoblocks and HF86 stereo amplifier. The HF14 may be the real prize- as it uses the same amplifier circuit and output transformer as the very well regarded HF81, and EF86. But with a separate power supply for each amp. This will improve isolation and deep bass response. Prices are starting to rise for the HF14, but a cheaper way in may be through the HF12, which is a mono version of the HF81, or an integratged version of the HF14. A simple rebuild to bypass the preamp stage and you have an HF14 at a lower cost.