Is there a difference between clip and playerclip? I've seen both used in maps, but they don't seem to do anything different in terms of gameplay.
No, blockbullets will stop players. Blockbullets is actually nodraw (i.e. solid to everything), except set to translucent so it doesn't block light or cut leaves.
Playerclip blocks players. Clips block everything except light (I think)
This. Clip Blocks players and NPCs, which TF2 is currently lacking, so it makes no difference at all.
IIRC:
- Playerclip: Stops players, allows rockets, stickies, sandman balls.
- Clip: Stops players, also stops rockets stickies, sandman balls, etc.
So the real choice is what you want those projectiles to do. I prefer playerclip for anything that has to do with "smoothing" the map out, because it means I can provide a wider or sloped area to walk on without confounding player expectations about what happens if they aim at a given spot.