In general, I use .25 for most guns, but .30's in my MK23 (propane). Slow (relative to .20's, say), but very accurate. .28's are a good compromise between .25 and .30.
Interesting, always used .25's for my guns. As they punch through the veggies better. Whats your thoughts on using a .28 or .30 in a gun shooting 430 with .20s? Ive never shot a .30 so I am curious as to how the trade off of speed to target vs accuracy is.