Yeah, FO is anything but "not really good". They have a lot of uses and can be really good in arena, at least on offence. They do require at least KRU's leadership zeta.
I have 3 accounts and I run NS on one, FO on another, and Sith on the 3rd. Of all those, my NS squad is the best, but my FO team is quickly catching up.
But I still wouldn't recommend either because it sounds like you're still a fairly early game player. NS don't have ships or lead to any legendary characters. You're getting a good raid team with some arena viability, which is good, but that's it. FO does lead to a legendary character (BB8), but Resistance is pretty limited in their use across multiple game modes and are really only good with Finn's zeta. So unless you're already farming zetas, they can wait too.
Empire is probably the best faction to go for simply because you'll get 2 of them with the team you're currently farming, you get a head start on another 2 that you get for free (Tarkin/TFP), and another from achievements you get just from playing the game (Vader). You can build them quickly and without competing for resources with other farms. They also have a lot of good ships and get you one of the best legendary toons in the game (R2D2).