Forgot to add about the guild store. I would say it depends. You can start on some good teams there. So it depends on what you want and where you're lacking which is everything because you recently started. Dengar is a decent choice. Reason being is he's a scoundrel and that will help with getting more credits as you'll need a team of scoundrels for that. Another easy pic for that is Cad Bane from the GW store. Finish Zeb first then I'd say go after Cad. I can't remember if you need a full team of 5, but more is always better. Again, full teams are the goal. Get Boba out of the Cantina store, he'll be your lead and is a good character for a while. Again farm him after chopper. If you do Greedo and IG-88 after Tarkin, you have a full team. This will also help you towards Chewie but that can come later.
If you're not liking that option, between the cantina stores and the guild store you can get a full clone team set up which is good. A few even have ships which is a bonus.
If you're not liking that option, you could do Geos/Sepratists. Poggle, Nute, Asaaj, Sun Fac, B2, IG-100, Geo soldier, geo spy and Grievous are are in the stores so you could throw a team together based on which stores you'd rather pull from and what team you'd like to create.
No matter what you do though, pick a path and stick with it. Set a goal of getting a specific team together and follow through. If you waiver between different teams you'll suffer and and the game becomes less fun then. Knowing when to switch over is good too though. If you start seeing another team regularly in arena, fleet arena, GAC or TW and you haven't started on that team, ask yourself what your plan is in that game mode. I'm starting to suffer in both my arena's because I took too long to move on to the next step in both and now I'm behind.