The 3G/4G Hotspot plan (10GB of 3G and 10GB of 4G) uses Verizon.
The 3G/4G Unlimited Plan uses Sprint.
If you are able to test Clearwire in your area it may be best going with Clearwire directly. Their plan is $49.99 a month for unlimited data, but it only includes 4G/WiMax, no 3G as backup.
It's also no contract you buy the hotspot up front for around $100.
Years ago you could successfully game on a Sprint 3G connection, but today, IMO, it's just not possible. Sprint's 3G network is so poor that it's hard to do anything with it, let alone play games online. I used to have a sprint mobile broadband line and could play my PS3 and PC games online with little to no lag, but ever since around the time the EVO 4G came out, 3G has taken a huge hit.
I haven't tried Sprint 4G/Wimax yet but imagine it should be fine for online gaming. I've tested a Verizon 4G/LTE hotspot and my PS3 and PC run great, no lag at all in any games. The problem is the 10GB data limit, if you can live with the limit then Verizon 4G is a great choice. Verizon 4G will continue to rapidly expand while Clearwire's WiMax is done, what you see is what you get there are no improvements coming.
When Sprint eventually gets a decent LTE network up I'm sure Millenicom will offer some sort of deal on that as well, but that's a ways off yet.
OP, I feel your pain. Although I am blessed with CenturyLink's 7Mbps "Power User" tier. LMAO
I'm only paying $29.99 monthly and when it goes up, I'm gone. The only plus is the 200 (or is it 250? GB cap) and they don't seem to enforce it other than throwing up a warning page at the beginning of the month if you really push it.
IIRC the cap on the 1.5 is 100GB monthly you aren't going to get a mobile plan anywhere near that. The 50GB one that Millenicom offers is SPRINT which sucks big time. As bad as CenturyLink often is, I still would not dump them for SPRINT or a service based off SPRINT. Just my opinion.
You might see if a faster tier is available, try retentions, threaten to cancel. May be able to get a really good deal for the same or even less than you are paying now!