I just went through this "debating the carriers" route last year when I switched from VirginMobile prepaid to a plan. (I wanted better phones.)
Sprint's main selling point for me is that unlimited data. When it works, you blow through data easily.
Just for comparison, I also have a Prepaid T-Mobile account (the $30 special). It gives me unlimited data (4G/HSPA+ speeds up to 4GB then throttles to Edge after that), unlimited texting and 100 voice minutes. I mistakenly set my photo app to auto-upload videos and pics while on mobile internet. I blew through my 4G cap in a couple hours. At least my only penalty was really crappy data speeds until my month reset a few days later. Had I been on Verizon or AT&T I would have seen an extra $10-$20 added to my bill. I doubt I would have noticed my error either until well after the damage was done. The stupid app was uploading MP4 TV Shows I transferred to watch on the go.
As long as Sprint maintains the unlimited data, they'll have me as a customer. Change that, and I'll go shopping.