That's kind of crazy because they are a re-seller and their service is on running on the network owned by the ATT, Verizon, etc. I maintain the fiber and copper circuits that feed the cell towers and I can assure you there is no such thing as a ST tower in any of the areas I serve. As far as I'm aware they are purely a re-seller which means they don't own their own network.
Most likely the problem with reception has more to do with buying one of their cheap phones. If you have the same phone there will be no difference from Verizon to ST or ATT to ST as far as the coverage and strength of signal goes.
Pretty sure my straight talk phone worked off the sprint network. It was on of those deals it worked great for the 1st year than got worse and worse. Wouldn't work at all at the hunting club. for the same price i was paying i went to verizon pre-pay and it has been much better for me.