Don't go to a chain. Lotus of Siam is an excellent choice and is nationally recognized as outstanding. With that size of a group, you could try many different dishes and I think it would be a great time. Look up the Red Rock Casino location and you can also have the experience of seeing that property. If you don't want to make that trip, there is the original location on the strip. Also look at Bootleggers for an old-time Vegas Italian experience. Food it very good and this is a short ride from anywhere on the south strip. Those are two experiences that your group could not get elsewhere in the US.