Gonna be as unbiased as I can and give them an 8. The stable did exactly what it was supposed to do and represent - show the past, present, and future of wrestling, and did a very good job of it. Orton and Batista became 2 of the first post-Attitude era stars, and you can never take that away from Evolution. Flair was invigorated, all 4 members took part in good and even some classic matches, and the Evolution theme is one of the greatest in wrestling, and exemplified everything you thought that stable should be.
Even though that is an 8, it isn't a strong favorable 8. Why? Cause Evolution was clearly a HHH stannery project due to his euphoric love for the Four Horsemen and Ric Flair, being an obvious massive adaptation of it. Also, well, that was the height of HHH's Reign Of Terror, and behind the purchase of WCW/ECW, that was the #2 reason fans turned away from the WWE in droves and started converting to UFC and MMA in general. Late 2002-2005, the majority of Evolution's run, it mostly consisted of HHH just beating the entire roster with no endgame other than to pad his legacy, a legacy that no matter how hard the WWE tries, will never stack up against The Rock and Stone Cold, and to a lesser extent, HBK, Undertaker and Mankind. I'll just stop right there as I've spent a lot of time in other threads about HHH from 2002-2005 (and honestly 2006-2007 even when Evolution had ended) and nothing more really needs to be explained.