I'd stick with the HMR as ammo is much easier to find. The WSM has a little better ballistics and less wind drift due to a higher dose of powder. WSM is around 3000fps and HMR is around 2550fps in the same grain projectile. But finding ammo for the WSM is a little harder. Even during then "ammo scare" .17HMr was still on the shelves and at normal pricing.
I have a Mossberg .17HMR I picked up at Academy a few years back for $180. Has been a great gun and very consistent shooter. Coons, bobcats and squirrels all agree on the accuracy and stopping power. All around 75 - 85 yards.