I switched to Straight Talk earlier this year when I had to leave a business account I was for over two years. I lasted exactly one month before I switched back to an AT&T plan with my OG L920. Poor customer service, no mms, worse coverage than on AT&T in the same area. Saving $20 a month was not worth it. Took alot of effort to get my mms service to work again after that too, bit that is another story.
Customer Service is not what it should be from ANY of the cellular service providers, this isn't an excuse in ST"s favor, but a slam against all of them.
As far as signal quality,
I don't see how you could notice a difference, since it's the same towers, leased from Verizon/Att/Tmo/Whoever and the only difference is a ST sim in your phone ?
I've personally experimented with two verizon phones, three tmo phones, and now four att phones on the ST networks for each. There was no difference at all in cellular service between the big carriers' service and ST's, other than the price paid monthly. I settled on a nice rugged ATT branded phone, with a straighttalk sim, and have enjoyed LTE since, without issue.