It's really personal preference and depends on how much you fly with that particular alliance's airlines. For example, I used to mainly fly on OW (in which I thought the logo was very nice, yet simple, especially the bolding) but now switched to *A (originally when flying OW: found it to be ugly and dark, but now: I like it).

I personally find the Skyteam logo weird without a symbolic meaning (OW is in a shape of a globe while *A is obvious).