Easiest is the front to a 14 as you won't need a new chain. Best is debatable. Rear up two or three teeth will net about the same change in gearing, but will need a longer chain. Most do the front. The only potential negative I've heard is that doing the front forces the chain around the smaller diameter so could increase wear. Lots have done it though and I haven't heard of any issues. Good luck and nice bike!