The very angry boy Menelaus probably edges his megalomaniac brother Agamemnon for the easiest 'beginner' faction. Neither of them have any downside in their campaign mechanics or their battle playstyle, but there's some nuance required in using Agamemnon correctly whereas everything about Menelaus is simple, straightforward, and strong.
Menelaus is the only leader who can use Total War's traditional global recruitment pool, giving him access to his best units from anywhere in the world in exchange for waiting a little longer and paying a little more to recruit them. On top of this, he can get his allies' best units too - an amazing advantage if you're buddies with, say, Achilles, who has the most and some of the best elite units in the game.
As ever in Total War, be wary about making alliances indiscriminately: if a defensive ally is attacked, you have to go to war against their aggressor, and if a military ally attacks someone else, you're obligated to join them. If you decline, breaking the terms of the alliance, everyone will know you can't be trusted. This makes it harder to agree deals in the future, and that's especially bad in Troy given how important bartering is in the new multi-resource economy. Call to Arms gives Menelaus a better reason than anyone else to forge alliances. Just be judicious when doing so.
The Spartan colonies mechanic enables you to settle any ruins that you can see without needing a local army, which is obviously amazing, but don't forget it also enables you to settle ruins in the usual way without losing any men from said army. This means you can raze cities for their resources and then settle them on the very next turn without waiting ages for your forces to replenish, so Menelaus can rampage through enemy territory without losing any momentum. Remember also that military allies give you their line of sight, so the ability to remote-settle means you can watch Achilles go around burning down cities and then nab them yourself before anyone else without even needing to be there. Seriously, Menelaus can be stupidly strong, and he's simple and fun to play. Recommended.
RELATED LINKS:
Total War Troy Sarpedon guide: start position, campaign mechanics, and unique units
Total War Troy Agamemnon guide: start position, campaign mechanics, and unique units
Total War Troy Paris guide: start position, campaign mechanics, and unique units