**note the sticky at the top of the forum that lists the stats for the dragons also has the information on figuring the post-tame skill caps.
Ok here goes my opinion, and remember it is just my opinion like anything your mileage may vary

I would continue to use Catharsis as a main dragon until a better one is found. My reasoning for that is basically this. Skill caps are unknown for any of them. Without knowing this I cannot truly give an accurate reading and can only go with the facts presented. Catharsis of the lot seems the most balanced and will provide a fine companion in your battles. True her HP's are not great but not bad either. Her skills are decent where they need to be (Wrestle and Magery) I myself would aim for higher in those two while also aiming for good tactics and resists. The other Dragons while OK would not have likely made it to my stables for various reasons.
Katharsis would have never passed initial inspection for me as the physical is way to low and Fire is not quite where I would like either. Not knowing what her caps are this reason would be why I would not choose her.
The un-named dragon from what I can tell the skills will end up being lower than I would prefer for my companion. While it looks like it is largely untrained and you will be able to probably figure caps that are relatively close to what they should be. Tactics and Resist both figuring with current numbers below a 110 skill when fully trained. That coupled with the really low fire resist means I would not have tamed this one.
Emperor would likely be my second choice for a companion as his resists are good and hp's are where I like them to be. That said the skills might not be where I would like them to be. Again not knowing the caps here really hurts but the tactics seems really low and wrestle seems to be not where I would like it either. suggestion on this one is keep it, train it fully and then compare against Catharsis.
Phalanx Looks like the best trained so far and looks to be nearing his caps. But his biggest detractor for me is the low physical.
My suggestion is to take a look at the stat ranges and skill ranges, determine whats important for you and what levels you find acceptable for each. Then decide what areas your willing to give a little in. Meaning if you set a minimum on your HP's of 980 and a Dragon spawns that meet most of the requirements you have set but this, do you not tame it? While finding that perfect dragon is a long and sometimes disappointing process, it does pay off in the end. Check all dragon spawn areas (Destard, Ilshnar, Fel side if your comfortable there) Personally I always preferred the Ilsh Valor spawn area.
Good luck in your search and hope this info helped somewhat.