Latias being one of my all time favourite pokes figure I'll throw in my 2c.
As a lot of people above me have already mentioned, including the OP, Latias can successfully fulfill many roles in the metagame, which is what makes it so great. I'm not a huge fan of comparing one Poke to another in these situations, as I think Latios and Latias really do serve different functions, but there are some comparisons which could be drawn. Latios is obviously the normal choice if one wishes to go the more offensive route, with its Scarf and Specs sets being some of the best Scarf/Specs sets in the current meta, or even its LO and EBelt sets can do quite a lot of damage. Latias can utilize sets similar to this, but as others have said its best sets tend to revolve around Calm Mind.
Back in BW1 my favourite Latias set by far was a BulkyCM set, which is still probably Latias' trademark set, although the metagame has changed enough to the point where now I feel there are slightly superior sets on many occasions. One set which I didn't see in the OP was the Choice Scarf set. Maybe thats because its shell is so similar to the Specs/LO sets, but I feel that I may as well post it here anyway.
Latias @ Choice Scarf
EV: 4 HP / 252 SpA / 252 Spe
- Draco Meteor
- Hidden Power Fire/Healing Wish
- Surf/Healing Wish
- Psyshock/Healing Wish
This set functions in a very similar way to Scarf Latios, although the main appeal that this set has over Latios, once again, is the surprise factor. Currently no one is staying in with Genesect against a Latios, unless they know they outspeed, because HP-Fire is just a little too common for Genesect's liking, and so theres no point taking the gamble of losing a serious threat for naught. Latias on the other hand is very rarely predicted to be running a Scarf, and while the LO and Specs sets are becoming a little more common, I feel this set is just as useful. In the aforementioned scenario against Genesect, your opponent is much more likely going to feel comfortable enough to either U-Turn or RP, only to be met with an HP-Fire to the general face area, and that won't be appreciated. Aside from the surprise factor another thing which this set utilizes well is Healing Wish. For those that don't know what Healing Wish does:
"The user faints. The Pokemon switched in next has its HP restored to maximum and any status conditions removed. The Pokemon enters the field at the end of the turn Healing Wish is used, so the Pokemon switched in does not have to take an attack. The Pokemon switched in will be healed to maximum before it takes any entry hazard damage.
This can be insurmountably useful if your sweeper is crippled, and would otherwise decimate your opponents team, think of it as a complete new lease on life. At first when I was running the Scarf set I really didn't want to give up any of my coverage moves, but through shuffling other team members around I had space for Healing Wish so I tried it out, and it can be just so damn nice. One example I'll provide; I was using a Sun team based around a Volcarona sweep, and it had gotten down to 30% HP, rocks on my side of the field, and my spinner gone. Because Heatran didn't do anything to the rest of my team, bar Latias, my opponent decided to play a lot more liberally with it, figuring that Volcarona was as good as dead. Long story short; I KO Heatran > Healing Wish Latias to Volcarona > Volcarona sweeps. This is just one example, and I'm sure many other people have had similar scenarios. Healing Wish functions best on the Scarf set because you need
to really get it off before your opponent if possible, avoiding a potential KO on Latias and losing the chance to give another team member a second life.
Just adding on to what Alk said; Latias is an incredibly useful check to the vast majority of both Sun and Rain teams, and in a meta that is completely dominated by the two, I think that makes it incredibly useful. Any one of the LO Tank, CM or Scarf sets does a great job in dealing with these teams, and that is what makes it so easy to fit Latias onto a team in my opinion, plus its so damn cute :3