Good 4th in this setup?

[Darwishy]

My friends and i recently started playing again, I am currently playing a Mag Prime and my friends are playing Frost / Nekros / Excalibur. Now i want to reroll in a warframe that would perfectly fit the 4th roll to do high level Excevations / Defense missions. I also want to be able to solo content when my friends are not online. Would Trinity be a good choice or would you suggest me something els ? Please don't give me the answer "play what you like"  because i dont know what i like in this game yet :P

[Marine027]

I suggest try all frames you can get your hands on, gettigna Slot for those isn't so hard as you think with farming relics and prime parts to get plat. Each fraem can be good for toher things in game, there is no real allrounder i say, a good setup for each mission with different frames can help, spy missions as example Loki, Ash and Ivara.

[Wolfglaive]

It depends on what you mean by 4th role. Trinity can provide energy to the other frames, so if that's an issue for your friends, then you may want to consider using her. However, depending on what you mean by "high level" missions, it looks like you're relying far too heavily on Frost's Snowglobe to shield the point, and aside from his Avalanche your team is lacking in effective radial crowd control (I say effective because Terrify and Radial Blind are helpful CC, but limited. Loki with a Disarm build would be good against enemies with firearms, while Vauban would be useful against Infested with Bastille/Repelling Bastille. Inaros can provide CC and healing with most of his kit, but unlike Trinity would not be able to provide your teammates energy. Volt can also offer a bit of extra shielding, though it's most effective on choke points and doorways, and he has a pocket CC in his number 1 and a large CC AoE for his number 4 which also turns enemies into a makeshift turret. There's a lot of possibilities, and since you have some fairly loose parameters, it's hard to pinpoint a perfect fit. 

[DanujCZ]

If you dont know what you like just go out and try stuff. We dont know what you like you have to find out yourself.

[(XBOX)ThermalStone]

It's good to have a crowd control frame.  Try Nyx.

[(PSN)lhbuch]

If you are going to get a frame that can fit many roles and also be self sustainable solo, I would say Rhino. He can be a buffer, provide CC and can be tanky.