I always prefer 30's over 29's, mostly because other people are unwilling to join unless they see a group of at least 4 x 30's. Having all 30's in a group makes people feel more secure. Anyone can pick up the relic, anyone can go into the portal without a problem, anyone can defend the left pillar at confluxes. I'm not saying that 30's perform better in reality, but in terms of reassurance for the team it's a whole lot better than having 29's.