About 356 b/c or "green dial" 911. Apart from the extreme difficulty of the corrosion issue, they are really two completely different cars. It really all depends on what you're looking for.
Although they are both old, I wouldn't say one is necessarily more reliable than the other. As you probably know, at that age, it really depends on the condition of the specific vehicle you're looking at. There's no question that the 911 will be a faster, better-handling and sportier car overall. For the price, I don't think there will be much difference between a restored 356 or an older restored 911T. Have you ever sat? I found the 911 to be more comfortable. I once sat in a 356 speedster and could barely tuck myself into it.