I have SPAN on my master bus by default. I have used Boogex in the past with good results, but I'm kind of a sucker for more "prepackaged" amp sims. You know, the ones where you choose the amp that looks like the one you'd want to play through? There's a lot of flexibility there, but that means it can take a lot of fucking around to get a specific sound... I've used MSED for a couple things, but M/S is a black art which rarely works out the way I intend. The Overtones GEQ is pretty cool, but unfortunately sort of limited by the non-parametricness. I haven't got a need for any of the others (I have a couple of their paid plugs, though) but in general all of their stuff is top quality.