Frame size is a very important issue, but don't stick to little details. That one inch will not really be the main factor of your final decision. You will be equally able to ride both with the right saddle height. What is very important Is for you to find and test some bikes around 17"-18" and choose one that will give you an upright riding position and won't force you to lean towards the bars to gain optimal control. Also keep that in mind: if you go for 29" or 27,5", 17" will be a better choice, but if you go for 26", 18" bikes will suit you better. Make a list with the bikes you are interested in, find sellers and test them. Don't be afraid to go for 29" or 27,5", 18" if you find a good bike. Changing a stem can fix everything. See ya on the trails!!