Can you guys tell me which frames are actually worthwhile/fun to play as? I just have Excaliber and Rhino right now... I was eyeing Frost/Frost Prime as my next build target. I hear good things about Nyx and Vaulban.
That's... hoo boy.
Everyone has their own playstyles, really. What I like and what you like, how I play and you play, could be very different. Keep that in mind with these suggestions. Also, when people say check out the wiki, they aren't joking. Check out the wiki. It's super helpful.
Frost/Frost Prime: A good alternative tank to Rhino, his damage output is higher but you'll rely more on mods for staying alive since you won't have the Iron Skin skill you have with Rhino.
The one thing to note here that is often overlooked is his
Snow Globe can backfire on you if you use a Stretch mod. Snow Globe creates a barrier that any character can enter, and projectiles can be fired from out of the globe at things outside of it. On the other hand, projectiles fired from outside the globe can't get in. If you get swarmed by melee enemies in a globe, and your allies are in the distance, you are pretty boned. They can't help you until they get inside the globe as well.
On a similar note, and this is just a general rule for globes overall, with or without stretch, positioning is everything. You can single handedly end a defense mission for your team if you drop one on an objective. You might think you are defending it from laser fire, and you are. But all the melee units that get up on that objective are free to wreck havoc with no means of stopping them other than melee combat on your own part.
Frosty is a fun frame, and a welcome addition to any squad, but you have a lot of responsibilities when playing as him. You're expected to drop your AOE ult when needed most, place globes in smart spots, and generally be a cool guy.
Vauban
I love this guy. Vauban can combo his skills with other frames skills fairly easily, creating neat and effective ways of clearing out a room. Built for dishing out damage, he can survive a fair amount as well, but his purpose is very much DPS. I find a shotgun with a good ROF mod suits him well, as he otherwise can't handle himself in close quarters that well.
Tesla balls are your bread and butter with Vauban, with Bastille being a very close second. Your balls stick to just about anything, including allies. Have an Ash on your team? Have him stand still, load him up with balls, and let him pop his ult. Watch the light show. Every time he teleports to a new target, the tesla balls will wreck havoc on any enemies standing near the poor guy getting stabbed.
Teslas aren't just useful as a utility, they are super spammable, and can be a great low-cost way to weaken foes as they come in from an entryway or catwalk.
Bastille is kind of like a no-risk Snow Globe. You want to have Stretch for this. All it does is create a AOE that lifts enemies into the air, where they dangle helplessly for a while. This is invaluable in any kind of defense mission, or just a situation where you need some breathing room.
Bounce is...it's a thing. You can make temporary jumppads that don't work well.
The ult is somewhat lacking as well, even though it sounds awesome. It'll create a tiny black hole, sucking enemies and players nearby towards it with a vacuum effect, and then exploding. It's not bad by any means, but there are far better ults in the game. That said, an explosive weapon blast in tandem with the ult at the peak of the collection can be pretty great.
Those are my two big suggestions.