I use Enigma on mine. Versus CoH, you're trading 65 resists for teleport, 45% fr/w, and more MF. I love tele (especially since I like using my zon for cow runs for socketable items and such, and tele helps me get to them before the trailing item stealers), and since my javezon is pretty far away from enemies most of the time, with my merc and valk taking hits, resists aren't really all that important to me. Plus, you could just make it yourself (breast plate if you want less str and more vit or archon plate for more def).
Teleport allows excellent merc control also (if he is holding Infinity).
But I'd say CoH is probably more useful in general. I've never found extra life to be terribly useful on my (PvM) javas and you lose a ton of resists, that need to be found elsewhere (usually charms, so less space is available for skillers then).