I've only recently become convinced by the argument for 0.25's in AEG's. Truth be told I still think that accuracy is so dependent on the wind that 0.25's only help up to a certain degree of breeze; beyond that you may as well use 0.2's because you're going to have to walk your shots in anyway.
I use Blaster 0.28 Stealth BB's in my pistol but, again truth be told, that's mainly because I have a bottle of them which have been sat around doing fcuk all for so long that I'm sick of the sight of them. I haven't evaluated how well they perform compared to other BB's properly, but they seem to be pretty good up to about 25m - I haven't fired it at anything/body further away.
King Arms 0.3's in my SVD and they have been great, except when it's blustery - I intend to try Blaster Devil 0.3's when I need more to see if their polish/extra QC makes a difference, but I really don't see the benefit of heavyweight ammo which you cannot see downrange, because how tf can you correct for wind if you can't see by how much you missed?
I suppose those who got their experience when Madbull still made tan 0.4's may be able to tell where they need to aim for various familiar conditions, but those of us new to the role badly need either a reboot or another company to take up the slack.