Surprisingly, I've found the Mint's speeds always comparable if not faster than T-Mobile. I did a speed test before/after I switched from T-Mobile to Mint, and Mint was actually faster (I ran the tests within 5 minutes of eachother).

Also, it was pretty amusing to get a voicemail from (a recording of) Ryan Reynolds telling me I could downgrade since I'm not using my full data amount each month.