Excel Biodegradable 0.25s, I like because they're reliable in both my AEGs and GBBs and come in lower-vis grey and black, rather than just plain white.
Also I <3 trees and flowers and fuzzy animals and shit like that.
On the same topic - has anyone seen the fluorescent 'tracer-style' pellets in a 0.25g or heavier form? Almost all the tracer pellets I've ever seen from every manufacturer are 0.12g. I'd love to mix those into regular usage in AEGs, but being barely half the weight they don't have the same flight characteristics.