make sure you also like the controls on your gun.
The controls on the benelli and remington are similar, with the slide release being in front of the trigger guard. The Benelli's safety is in front of the trigger, on the guard, with the Remington's being behind the trigger. I can't remember exactly how the winchester controls are, but I'm sure someone else can comment.
More importantly, make sure that your gun fits you well. The Nova is an excellent gun that rattles a bit (I have one, and you can do a search on my posts on the gun), but you need to make sure it fits you. The receiver is longer than the 870. This makes the Nova's overall length equal to a 20-21" 870. With that length on the 870, you'd probably have a Rem choke barrel. With the Nova, you're stuck with cylinder. The Nova's butt pad is a little wider than the 870, and I've noticed I can fire off 4 boxes of Walmart 7 1/2" birdshot with a few boxes of various 00 buck and brenneke slugs without any ill effects. I feel a little more recoil on my wood-stocked 870's when duplicating this practice. I am using proper form, so this is my observation when using the guns in out-of-the-box setup.
You can check the various manufacturers for comparisons of each gun's specifications. I'm pretty sure I've gone over them before, you might want to do a search.
One thing that I like about the Nova is the Magazine cut-off and the ease of unloading. The mag cut-off allows you to load your whole mag with buckshot, and then in the middle of firing, you can throw in a slug and fire it (providing you've determined your change in POI over buck shot), and then got right back to firing your buck shot. I practice this drill a lot at the range. It helps me with my port-side loading (which the 3.5" opening really facilitates) If you want to unload your Nova, you just press on the bars in the reciever, and your shell will slide out of the bottom. You don't need to rack the slide, to kick out a shell.
The 870 HD would be a nice gun because you don't have to worry about the magazine dimples (are they still doing this? I haven't gotten an 870 since '03, I think). The Nova's 2 shot extension actually turns out being 3 when you use 2 3/4" shells the 2 shot is when you use 3 1/2" mags.
The Winchester is a fine gun as well. It's got a pretty fast action, and keeps my brother happy. I like the 870 for it's steel receiver, though.
I own 870's and a Nova. I can go either way on these two, but the 870 has more going for it if you want to get it to fit you better, or, if you must, accessorize.
All in all, get the gun that fits you best (I can shoulder my shotguns with my eyes closed and then open them with my sights right on target-that's how I like mine to fit), whose controls you can operate in the dark, without fumbling, and shoot as much ammo to equal the cost of your desired add-on.
edited to include mag-cutoff button and unloading for Nova