T-Mobile at the moment is vastly better than att. T-Mobile hspa+ speeds are faster and more consistent. Up to 42mbs on T-Mobile and 22mbs on att. Also T-Mobile has the fastest 3g network, meaning you'll never have to worry about speeds. I can testify to that.
I am on AT&T with LTE. I get speeds surpassing what you just posted for T-Mobile, easily. I also have unlimited data on AT&T.
Also, the T-Mobile plan typically referred to only offers 100 minutes a month for calls