Having owned both corded and cordless, 10" & 12", single bevel and dual bevel...here's my take:
My previous miter saw was a 12" single-bevel, non-sliding corded Ridgid that I used extensively for years. At the time I bought it, I couldn't afford a slider, so I got the bigger blade to handle bigger material. IMO, the slider makes up for blade size; most people don't need the big blades any longer. My 10" Makita cordless slider will handle everything my 12" did, and more. Given the size, weight, and cost of the 12" sliding miter saws, I don't see the need except for very specific jobs.
If you plan on only using your saw in one fixed location in your shop, go corded. If you have any intentions or possibilities of needing to move it around to be closer to the work, go cordless. Cordless miter saws are awesome and easily the equal of their corded counterparts these days.
As always, if you go cordless buy the saw that fits into your battery system (if you're already invested in cordless tools.) I bought a Makita, since I was already invested in the system. (Though their slider mechanism makes for a much more compact saw than others, so if I'd been in the market for a corded version I'd still have bought Makita.)
Over the years I've found the best accessory purchase (other than blades, of course) is a mobile miter saw stand. Not only can I move it around my garage, the stand makes it easy to transport to the job. I take the saw to where I need it once, rather than carrying wood all over the place every time I need a cut.
