By Fenrir.Schutz 2010-11-10 18:29:32
It's kind of hard to pick-and-choose the type of mob to skill up on, because SE seems to only put in one "optimal mob group" (that hits a nice yellow/orange range) for any given Rank range in an area...unless you are willing to travel all around the globe, that is.
I tend to think that any mob that gives great Sword skill up ranks (yellow/orange/red) will consequently give great Sentinel skill also. It just so happens that at that Rank range, Dodos are universally the best for you, even if they happen to do annoying moves that won't skill up your shield at all (like those status-effect Belches.)
Once you get to Rank 10 Sentinel, things get a bit easier at least with Aegis Boon 1. This will let you consider taking on tougher mobs instead of shying away from them. Also, always using Still Precision (and removing evasion+ items) tends to help as well for shield defense procs. If you really are all-about-shield-skill ups, there are always those other tricks like using Conjurer Stoneskin/Cure spam, and/or Thaumaturge Stygian Spikes to sit there and milk opponents but naturally those require time investments of their own if you didn't level those jobs.