My favorite size Glock is the 19/23 size, but I do have a Gen4 G30 that I do carry. Basically they feel like a slightly shorter, fatter and heavier G19/23. I carry mine OWB in a Don Hume JIT and it carries quite well despite it not being a very small gun. I have a G21 Gen4 too but it feels thinner than the G30, mainly because the grip hump begins sooner on the shorter gripped G30 than the G21, making the G21 feel thinner gripped, even though it isn't.
I will say that the G30 of mine is highly accurate and a superb shooter, it gets my vote for the most accurate Glock. Overall I like the 21 better, but there's no denying the 30 is fantastic, even if it's a bit chunky.