What sliding miter saw should I get Ridgid 4210 or the kobalt 857242?
I recommend Ridgid over Kobalt, but wouldn't buy either of them if I was in the market for a saw. I'd get a DeWalt - and did. Even though it cost more than the Ridgid available at the time, it was better enough to be worth the extra money. That was 15 years ago and I still have it.
IF money isn't an issue, get the Ridgid.