Hey guys an update on what I did.
I just got back and found an OK deal. I'm not sure what you guys were paying for Sprint, but I was paying (after taxes and surcharges) 160/mo. for two lines, unlimited data + 2k non cell-to-cell mins and unlimited everything else. I ended up going T-Mobile and it's looking like the bill will be around 130/mo for 3, not 2 lines. One will have unlimited data, the other two are basic flip phones. Everything else is unlimited.
After bugging the living crap out of the representative and asking repeatedly throughout the sales process, it seems like they have a more flexible, less technical data plan. If this is not true, I'll necro this thread sometime to let everyone know.
Although the 130/mo for 3 lines looks good on paper, I did have to put down (after taxes) $430 for the three phones (GS-4, x2 basic flip phones) - not a pretty amount. After bugging them about how much it cost, they at least gave me a zagg screen protector and some crappy.. body armor? body guard? phone case. Not bad.
I mentioned my usage with tethering in the original post. Should things go sour the same way it did with Sprint, I'll update this thread and let everyone know what happened in detail. Supposedly the rep at the store was an avid user for tethering as well, though he only hinted it, telling me there's little for me to worry from his 'personal' experience.
On another note, I did have an incident with Sprint in the past. My phone was evidently set on automatic connection and Sprint literally kicked my phone off the plan for something they called 'excessive roaming'. They claimed they sent me a warning letter beforehand.. and I'm sure they did. My desk is a mess. The guy over at T-Mobile told me roaming was truly unlimited, but I won't take my chances just in case.
Data speed differences in the Denver Metropolitan area are significant. Speed Test shows around 1.5mbps DL Sprint WiMax, 8.16mbps DL T-Mobile "LTE" (Someone told me T-Mobile LTE isn't 'real' LTE. Not sure on this). 10 tests each were done and averaged. 5 tests indoors, 5 tests outdoors.
Thanks for the responses/input - it helped me make my decision. This forum has always been nothing short of awesome.