They are all super expensive...most of my reading showed people like Red, Red-black and I have heard some of their silvers and Golds as well. I can say that Synergistic Purple and Orange are very well regarded. Sablon Audio uses them...which we have...and they are 200 or less. Still expensive but very well regarded.
In my experience with QSA fuses and CH precision--The mains fuse is about 70% of the performance and the stand-by fuse is about 30% of the performance. So, if you are wanting to maximize performance while keeping budget in mind then select a stand-by fuse that is a level or two below the mains fuse.
The break points for me are:
Mains / Stand-by
Yellow / Yellow - a huge no-brainer for all CH gear. this is a little over $400 and a very nice drop in noise floor. how else is someone going to spend $400 on their system and achieve this?
Violet / Yellow -- Big step up over the yellow in the mains. Another big noise floor drop. CH is starting to sound very nice. The total cost here is just over $900
Black-Red / Violet -- This is huge. Really remarkable decrease in noise floor. Resolution goes way up but the sound becomes even more emotional. This is about $3500.
Everyone gets hung up on the fact that these are fuses and they are so "expensive". I used to also get some heartburn over this, but once I experienced what they do there was no going back. However, let's put this into perspective.
A P10 is about $75K. So buying and installing two yellow fuses is 0.5% of the purchase price. Buying and installing Violet/Yellow is 1.2% of the purchase price. Buying and installing a black-red / Violet is 4.6% of the purchase price. IMHO, installing the aftermarket fuses improves the performance well beyond 5%.