Both datacenters feel empty after the split. From what I've seen the chance to find a pug group in pf for savage/extreme is almost the same on both DC.
On Chaos you may have a slightly better chance to find a raid static since Cerberus and Ragnarok still have a good amount of raiders while Light only has Odin as a populated raid server (as far as I know at least, lots of people have been switching servers since the split). Keep in mind that Chaos does have more french people (stay away from Moogle).