Cell phones forum: Should I ditch Sprint for T-Mobile?

I used to be on my dad's ATT plan, but he suspended the account and nixed my unlimited data and I moved to Sprint. Now I kind of have buyers remorse because they embed their SIM cards, get terrible signal inside buildings (being a non VZ CDMA carrier) unless you're right next to a window, and have a slow 3G network, and are taking forever to get LTE up. VZ is not an option, its too expensive, altho its by far the best network. I'm thinking of going to T-Mobile, because their 3G is HSPA+, which is kind of 4G, and LTE gets bad battery life anyway. They also have unlimited data, and I feel like even if I got to the point of throttling, it might STILL be faster than Sprint. I also like the idea of GSM too. But T-Mobile is going under and I wanna know more about their service.

I'm in Eastern LI right now, and probably will be in NYC later this year. I do still own a Photon, which I could use for overseas if Sprint doesn't update their GS3 like Verizon will, but I don't wanna bother owning 2 phones. Helpppp!