I generally feel the 'best system' is the one that allows for the best gameplay, and generally as a GM I'm looking for one that many people already know, that totally newbs can learn fairly quickly and will not have to forget entirely if they move and wish to join another group, and so on. GURPs just doesn't do that so well, it's also the kinda Linux to D&D's Windows or DOS. If I find a group where most people know GURPS and the others want to learn, great, I'd say the same for any system, but in general, if someone ask me to run something with a newer group or where the inclusion of new or short term players is probable, I'm gonna go with D&D 3.5, I'm not a big 4.0 fan but I'd run that before going to an alternate system like GURPs or Palladium or White Wolf. Now, White Wolf is probably the easiest major system to teach new players but there are a fair numbe rof smaller ones, like Warhammer's various RPGs, which tend to allow quick generation and easy play, so even if I was running a one shot or short tem campaign I'd rather go with those than GURPS, and any long campaign I'm likely to go with D&D's most recent incarnations, at least for fantasy, outside of the swords and sorcery stuff I'm fairly amenable to using GURPs but I'd probably pick appropriate to the setting, Shadowrun for Cyberpunk, Palladium Rifts for cheezy high-tech post-apocalyptic, etc.