Blue
Ravenous Bugblatter Beast of Traal
These Essentials guys look declawed, in terms of balance. They just look weak all around. Sure they're losing flexibility of Stuff to Do and Stuff to Choose From... but what are you gaining by giving that flexibility and options up? It just looks like a Regular character that chooses to just use Atwills and Dailies.
Where's the payoff (or balancing factor), mechanically?
Mechanically they are on par with per-Essentials characters. To talk strikers for a second: you can't eek out quite as much on the high end, especially novas, but in general they are very reliable at doing great DPR round after round. And it's much harder to build a bad essential character. The other essential characters I've seen have been about the same for their role - more consistent/less bursty, reasonably on par. (Though I haven't seen paragon or epic play for any of them yet.)
You're not going to handicap yourself mechanically either way and they play well together in parties. If you want to go 4e core or 4e essentials for your PC to me depends more on your play style. More straightforward character design and play - go essentials. More choices both at the table and off, go core.
The biggest balance difference that I can make as a generalization is that Essentials always seem to bring their "A" game while core classes sometimes take it easy (use no dailies, etc) and then at other times open up a can of whoopie on a really hard encounter spending lots of them.
I'm playing a Runepriest in one game, arguable one of the more complex and finicky classes mechanically and loving it, but if that character dies my replacement PC might be a Sentinel, the essentials druid leader who's very straightforward.