Almost ANY stock will be an improvement over the "Gumby" stock that Remington ships with the SPS tac's.
I have no experience with the Magpul but what I've looked at is impressive. I personally use the B&C Medalist "Tactical" A-5. Similar look and construction but it includes an accessory rail on the bottom of the forend. Makes for easy adjustments of sling attachment points and bipod position. Being able to move a bipod forward or back can help greatly in the balance of a firearm. All the way forward for LR shooting and back a ways for critters that may be running across your field of view and require some ability to swing the rifle easily.
The B&C is almost twice the price but has a lot of good, usable, features similar to the Magpul. I think the real differences will be in materials with the B&C being a solid composite "layup" and the Magpul being more of a molded product using parts/pieces from their AR line-up. The Magpul is 3# and the B&C is 5#. That extra 2# translates to a lot of "sturdy" and "recoil absorbing".