I would rather go with the i5-3317u. The base clockspeed is 1.7GHz which is 100MHz lower than the i3-3217u. However, when Turbo Boost kicks in the CPU can go up to 2.6GHz if only one core is being used and probably 2.4GHz if both cores are used. That can be a significant difference in performance especially in the future since everything generally becomes more CPU intensive.
It will be much more easier to replace the HDD with a SSD in the future, than it would be to upgrade the CPU because the CPU is soldered into the motherboard which basically makes an upgrade impossible.