From best to worst imho: RF - Bouncy - Seekers - Toaster - Blaster (- Pepper - Electro - Freezer)

That's right, i don't like seekers that much at all. I even have a tendency to leave the powerup out of most of my levels. Pepperspray is far from worthless. Though it can't be powered up, it's nearly impossible to see it coming, and it has quite a decent range and speed if fired while running.