I have both the Stevens 200 and Mossberg ATR as well as a Savage 110. I like them all the same. I'm very impressed with the accuracy and performance of the Mossberg. Each account I have read of the Mossbergs accuracy has been superb, including magazine tests. My own results support what I have read. Neither are without their faults. Both have their advantages. Between my hunting pardner and I we have (3) Savages, (3) Mossbergs and (1) Stevens (with another ordered and on the way). Both of us have shot all of them many times and have experienced no problems. You are correct in that the Mossberg is not offered in the 7mm-08.
All of the previous reasons to go with the Stevens are true and sound advice. A disadvantage of the Mossberg is the lack of a proven background. Its roots can be traced to the Charter 2000 rifle, but even that didn't make a big splash in the market before it's demise. What the Mossberg does have going for it is that they use E.R Shaw barrels that have a recessed crown, are free floated and have a receiver design that has been reported to be a close copy of a Howa action. It is provided with scope mounts, but those designed for the Vanguard (Howa) or Rem 700 will work.
My own feeling is that the Mossberg stock is more rigid that the Stevens, which is subject of many complaints due to it's desire to flex. I have also read of issues with the magazine follower on the Stevens. I did have a feeding problem on mine, but it was related to an improperly installed follower. The Stevens trigger can be adjusted and there are instructions on the 'net on how to do so. The Mossbergs trigger can be adjusted, but its a difficult process. I seem to recall reading that someone was able to do so, but it was not an easy task and involved replacing a part or two that will be damaged in the dis-assembly process.
The Stevens does have the capabilities to be customized. The barrels can be replaced and there are many aftermarket parts available. Go to
www.Savageshooters.com. for tons of info on the Savage and Stevens.
The Mossberg does have a molded trigger guard and sling mounts. I have read one account where the trigger guard has broken. However, the Mossberg is offered with a checkered Walnut stock on the short action models. The trigger guards on those versions is a separate unit.
My view is that the decision is a toss up. It comes down to the individuals preference and what is important to them. I like them both. I tend to favor the Mossberg primarily because they are much less expensive in my area than the Stevens and the accuracy is just flat out superb. The Stevens has an unquestionable reputation being of a proven design. Both have their share of plastic.
Good Luck with you choice.