I like the 7mm STW but there are a couple things to consider here. 1. For some reason brass can dry up and be **** near impossible to find for the 7mmSTW at times. I believe it is not long for the standard production list. I think it will always be made in a "seasonal run" but its becoming a dead stick. I think Remington bought the rights to the 7mm STW just to kill it to get ready for the release of the 7mm RUM. Just my opinion.
2. From a rifle builders stand point, the beltless case design is far superior. The reason is because the belted magnum cases have a wide range of belt thicknesses. This variation eliminates the possibility to fit the chamber as tightly as you would on say the RUM. The thin shoulder on the rum can easily be set back a thou or two for easy chambering, the solid belt on the STW cannot be moved and if it contacts the barrel solidly, you will get accuracy issues.
I had serious problems with the first couple STW rifles I built many years ago. Set them up, they shot great, send them to their customers and got calls back that their brass would not chamber. Seems from brand to brand and even lot to lot, headspace specs on the belted magnums can be up to 15 thou different which means if you set a barrel up for the shorter headspace, the longer brass will not even chamber!!!
Not a huge issue, you just chamber the rifles relatively loose by an accuracy minded smiths standards and then once you fireform your brass you then transfer headspace chores to the shoulder. Still, its just a bother which is not there with the 300 RUM.
Between the 7mm and 300 RUM. I would probably go with the 300 simply for longer barrel life. The 7mm RUM is a great chambering but its in the velocity range that the very best LR bullets may start to have problems with accuracy at its velocity potential. With the 160 gr Accubond, its full velocity with no problems but the 300 is better suited for heavier game because of its larger diameter and heavier bullets, plus longer barrel life. While I LOVE the big 7mms (obviously with my 7mm AM), I would probably still recommend the 300 RUM to you.