Infernape and Blaziken are both solid choices (in fact, as of generation 4, my friend (who is an INCREDIBLE PokéNerd (moreso than I)) recommended me to use an Infernape).
Being Fire/Fighting, they are able to counter many of the Latis' common weaknesses: Ice, Bug, and Dark. Really the only thing remaining is Ghost (The Latis can take out most Dragons themselves). Well, if you dont want to waste a moveslot on your Lati, Shadow Claw (TM65 is always a viable choice for either Infernape or Blaziken).
The choice between Blaziken and Infernape is up to battle style, I guess. Blaziken hits harder (both in SP.ATK and ATK), but Infernape is a lot faster.
I personally prefer speed over strength any day, so I go with Infernape desu~! ^_^; Also, Blaziken/Infernape are better suited to stay alongside Latias, because those hard hitters complement her defensive battling style.
Like I said before, Skarmory is also a decent choice; good for Latios. If you EV up his SP.DEF, he can take ice attacks better as well, and he can take out bugs without breaking much of a sweat. All thats left is dark and ghost, which he is well-resistant to. With a good Annoyer/Wall moveset, Skarmory can hold his own in battle, chipping away the opponents' hp, while Latios moves in for the kill. (Figuratively speaking pplz! xD)