I've done Echo Canyon but never the Cholla trail. Echo Canyon was pretty cool, and it's also easier to find a place to park which was the main reason I picked it. Hiking the summit is very popular, so get there early if you want a parking spot. Also, we ended up starting in the afternoon and it got dark on us part way down. That was a mistake, on that trail it would have been easy to slip and bang yourself up. We made it back ok but next time we'll be starting earlier in the day.
The best scenery is up near the summit where the trails come together so you'll probably be happy with either one.