This a tough question, but I'm kind of tempted to opt for the iPhone 6.
There are two main reasons:
Early sales figures seem to show the iPhone 6 outselling the 6+ by quite some margin
I haven't got the pockets for a 6+
I'd also add that, because I already have a tablet, the 6+ seems like it'd be dangerously close to making my tablet redundant... So I'd have to opt for the iPhone 6 just to keep my tablet feeling loved.
Although... Apart from reading or watching Netflix before bed, I hardly ever need such a large screen anyway to be honest...