When I look at the Summmon Monster IV list, the Hound Archon seems significantly more powerful than the other options. He has 2 fairly powerful constant auras, SR15, constant detect evil, some decent spells and the change shape ability. Plus, if you compare base stats to something like a rhino,he has more attacks, similar DPR and only 3 less hp. All of this makes the Hound Archon seem a bit out of place. Opinions?
I'd compare the hound archon to a celestial/fiendish bison. The archon has better DR and SR, but generally worse attacks (the bison is a real heavy hitter). The protection from evil and aura of menace are pretty good, though.
He is powerful, especially against non-evil creatures. The DR 10/evil makes a wonderful temporary blocker for a wizard. (I happen to be planning on using this technique in a mostly wizard society game on Friday)
I wouldn't go as far as to say it is significantly better. I don't have my books on me to double check, but can't S.M.4 pull up any Mephit as well? While physically frailer than most things on the list they grant amazing versatility in the form of a hundful of lower level spell duplication (invisibility, mirror image, gust of wind, and scorching ray to name a few off the top of my head) as well as making good scouts or spies. Also while I don't remember any specific abilities without something to reference, doesn't the bison or other such creature on the list get Trample where as I don't think the Archon gets any area of affect attacks? Plus the Templates are nice to add onto the base animals because I believe their smite work as the paladin's, unless I'm mistaken. It all depends on the purpose for which you are casting the spell.
Of course I'm a fan of the personalized summon list where you pick one monster per level to add to your list of possible summons and get stat cards made for each as a quick reference. Speeds up play and can add a lot of flavor to a conjuration heavy caster while taking out a big chunk of unexpected solutions to a DM's planned puzzle.