Considering jumping from AT&T to T

Im considering jumping from AT&T to T-Mobile for a few reasons, but I do have a couple of questions (for SoCal users in general):

1. On the family plans Along with 2 lines – how much are the typical monthly fees/taxes? $80 – $100 plan for 2 line range
Im currently at $116 for 2 lines on AT&T, which is ok considering I have a corp discount to get me to that low (25%) title=Stick.

2. I know that T-Mo uses the old Pacbell sites (which were very good), and Rootmetrics shows it as well… but how good in general is coverage/capacity in San Fernando/Santa Clarita valley areas

3. Roaming – I hope not to have this too often, but in a few places, I know this will hit true – Northern MI, Bozeman Montana, etc. Is it restricted to 2G, or just 2G speed ?

4. Do I want new(er) gear ? Samsung SGIII has only band 4 and 17. iPhone 5c has a bunch, as does iPhone 6. Sounds of Band 12 have me concerned.

Since AT&T has killed the subsidies, T-Mobile in some ways is actually cheaper/better for me… especially when I go to or call Canada (free data roaming / sms – even if its slow is priceless, also, $0.20 for calls vs. $1.00 + $30 on AT&T – this alone could save me a lot this summer).