If you need an instant A/B comparison to hear the difference between two different tubes, go with the cheaper tubes.
Better to give each tube a couple of days in your component due to warm up, breaking in, and general settling. Pick a couple of well known, well recorded pieces and take notes.
If you can't really identify any significant, to you, benefits of one over the other, then go with which ever is cheaper.
Tube rolling is not as easy as component selection in many regards with its virtually instant A/B comparison abilities. I put it more in the lines of IC and cable "rolling". Most changes are going to be quite subtle and take some time to familiarize with while other changes may be more apparent from the beginning, but take time to recognizes all the differences (other than just the obvious). Try to control some of the variables though, like record your volume settings for a piece and replicate that setting when trying a different tube (at least during part of the analysis period). Also do this with an SPL reading, which may end up that you have to change the volume control setting to equal the same sound levels between different tubes. If you are like me, you probably listen at two different volume settings (very general), one moderate and the other loud (depending on my mood and who is around/asleep/doing homework, etc. . ) and compare at both the more common levels. Ultimately you want tubes that are going to deliver what you are seeking at your normal listening levels.