Not much of an evangelist for anything, though like Pat I like some thing for what they are even if they aren't a good fit for me. Besides, my system tastes have changed too much over the years to not appreciate "this thing I used to like I really had a lot of fun with at the time but now I'm not interested in doing that anymore".
The closest I come is thinking that BEMCI/RC is sometimes better than it gets credit for (and all of its related off-shoots, ditto), and that Toon and Dragon Quest are under-appreciated for what they do well and how they work (even if they both are somewhat narrow and thus won't appeal to a lot of people for that reason, plus DQ definitely has some warts). When people get excited about Traveller, various RQ versions, GURPS and Hero System, etc., I can see it, even though I don't (currently) share it. I'll hum along, but I'm not going to start the hymn.
There's also a fairly long list of games that I'd probably be at least a little more enthusiastic about (if not quite evangelical) if I had the opportunity to experience them as a player. For various reasons, they don't make it high enough up the list for me to invest in them as a GM.