I like the S5, but Samsung has hinted that we could see a Galaxy S5 Prime later this year with a better camera and more options.
With that being said, my next handset will be a Note 4, probably on AT&T.
With T-Mobile raising rates to $80 for Unlimited for your first line as of 3/23/2014, it appears that I will be switching to the next best Carrier that is not Sprint. I wanted to give T-Mobile a chance, but with spotty coverage and price increases, I can't support this any longer.
AT&T's 10GB Data Share Plan for $130 for 2 Lines with 4G LTE in way more places than Sprint has in my area sounds like a good deal.