famous and oldest sites with altcoin are fortunejack and bitsler. There are many other sites too but I trust these two the most.
Yea, time on the market is a good way to gauge a site's stability, and also if its legit and reliable. The two you mentioned are very good and i second your comment. I'd also point out to jetwin, the one i'm taking part on a signature campaign. They seem to be starting going in the right path, definitely worth checking it out.