Groover 101 based on my experience. I have grooved on all of these on at least one river trip. All of these are available from Cascade Outfitters so the prices are from their website.
Johnny Partner - $587 - the Cadillac of groovers. Expensive, a bit heavy, will withstand years of use and abuse.
River Bank - $369 - sturdy, stable, nice. Only used this once awhile ago, so I don't remember too much about it.
EcoSafe - $190 - lots of folks use these and love them. Requires a rocket box. I have used these many times. Sturdy, easy to secure on the boat. Not my favorite.....don't like the rocket box, find them tippy, don't like the small "poop chute" design. Just my personal opinion, lots of folks use and love them.
Pett - $117 - I have seen one, but never used one. Not accepted on all rivers? Uses wag bags.
Bucket with Gamma Lid - $50 for the Restop, or $20-$30 if you make your own. This is the system I have used for the past 8 years. Simple, easy to make and use. Easy to clean in a scat machine, slightly more challenging at an RV dump station. Not accepted on the Grand Canyon. We have used this on the Salmon, Middle Fork, Snake, Rogue, Deso, San Juan without problems.
These are the ones I know about. All of them work fine. Just depends how how much you want to spend and where you will be going (Grand Canyon). Folks will chime in on their favorites.