What I don't get is this:
When you run speedtest it sends packets to a particular server and back to your phone measuring its throughput thus giving you theorhetical speed your phone is capable of. In no way does that measure real world performance. Sure, 48Mbps is a hell of a lot faster than 1.5Mbps but if you visit a site that's set with limited bandwidth (most sites do) to keep costs down, both phones will down load that site at the same freakin speed. If one is faster than the other, then that is limited to it's processor and GPU rendering of that particular site. The same principle applies to phones and PC's alike with broadband service.
Hook two PC's to a router with BB service. One PC has a Phenom II X6, 8MB pc1600 ram, ATI 5870 GPU, and a 128MB SSD with an indalink controller. The other PC has a pentium 3 proc, 2MB pc800 ram, Rage Pro 128MB graphics controller, and a 500GB WD with 2Mb cache. Now, run them both at the same time at the same site. Sure the faster PC is going to load the site faster but the other PC is going to load it too. The difference might be 2 to 5 seconds. Now run youtube. Sure the faster PC is going to load it faster but the slower one will load it also. Both will play...but neither should buffer, and if one does, it's because the packets being received are taking longer to register. But BOTH PC's are receiving the packets at the same speed......!!!
Point is, if a phone loads a freakin webpage 2-5 seconds slower than another, so-what. If 2-5 seconds of time feels like an eternity, or you need a phone that downloads an app 3 seconds before you actually download it, then I suggest you write your congressman asking for instantaneous broadband service.
For what its worth OP, I get 400kbps to 800kbps on 3G (no 4g here) and youtube rarely buffers unless it's at peak times. I suggest you do your research and find a carrier and phone that suit your needs catering to youtube because it's obvious Sprint's not doing it for you.
Peace.