Las Cruces is definitely prettier than El Paso. If you go to La Posta, take a side trip to the Spotted Dog Brewery. Its only a few blocks away on Avenida de Mesilla. I've been drinking Jerry's brew for years, long before he went into business.
Carlsbad Caverns is a must do if you are in this part of the world. There really is nothing like it. They were shut down for a couple of days due to a broken water line, but it has been repaired. The road from US 180 up to the park has some tight curves, but you should be ok. You will go through a Border Patrol checkpoint east of El Paso on 180 or I-10, so have your travel papers handy.
