Considering all the factors, stats, abilities, types, skills,

First step of being competitive, don't rely on fucking ubers. second step, go to the battle tree, get your shit kicked in a bunch of times and tell us what you learned. If you're serious about this t hen get to it, and don't do the ultra beast quest yet

>>30800180
I've had the most ___fun with Buzzwole and Magearna.

>>30800210
Already got Solgaleo, Tapu Koko, Magearna, Necrozma, and the beasts. Figured I'd need them for battle tree from what heard.

>>30800210
>go to the battle tree, get your shit kicked in a bunch of times and tell us what you learned.

The fuck? My ten year old cousin is doing ok with the battle tree how is that supposed to teach them anything when the AI is dumber than a box of rocks?

>>30800180
Anybody?

Tapu Koko
Magearna
Buzzwole
Kartana
Xurkitree
Solgaleo
Guzzlord
Nihilego
Necrozma

And whatever else I haven't caught/traded for yet.

It depends what team you're going for.

I use Tapu Lele.

>>30801418
Look, if you want to actually understand the game (at least singles, though they have a pretty good doubles community now too), you should probably just go to smogon. Copy a team by someone who's good, practice using it in the simulator (pokemonshowdown), and try to figure out WHY it works. Then you can build your own team once you figure out what makes teams good and what people generally use.

>>30801474
This.

If you're just starting out, try sample teams and figure things out first, then you tweak it according to your preference, maybe swap 1-2 mon to fill a different niche, maybe put in a rare pick if it fits your team well.

Smogon has a lot of resource on sample teams, just pick the one that suits your style best. Good players will rarely lose to a copy-pasted template teams tho.

If you're asking which legendaries are good, then my suggestion is to listen to >>30800210 and figure out how to break the AI, then start building a team. Learn to build a team and learn to predict before relying on ubers (kartana, pyukumuku), then start making a team and you'll know who to add.