No experience with TalkTalk, but I put my Granddad on Virgin ADSL well over 18months ago now (back when I was a happy Virgin Cable customer) and in all honesty it has been flawless as far as I'm aware. He has once mentioned to me about a slowdown on an evening. They also upgraded him from 2Mb to 8Mb for free (didnt tell him mind, but gift horses, their mouths and all that).
Surely tho, if your looking at ADSL, why are you limited to TalkTalk and Virgin? Every ADSL provider uses the same BT infrastructure and in a perfect world, the speeds from one supplier to the next should be equal. There are much better options for standard ADSL than Virgin and TalkTalk...
Have you tried
www.samknows.com yet? You might be surprised. I'm in "the countryside" too and we've recently joined the 21st century with O2, Be*, Sky, etc, all treating us!