Really depends on the Quality of your guests.
If its mostly Lubbers the push button electric unit will be worth the extra installation , trouble shooting , repair, expen$e and occasional dead batts.
If its mostly boat folks a QUALITY (not the $99 Jabsco),, a Groco K or Skipper would be my first choice.
If its a split decision a Lavac with a better (edson) pump for waste would be just fine.
Usually it can't be plugged (with edson pump) so a pail of water and it will be back in action with zero effort.
Tossing cat waste , hard cigars,may require the water.
OF course if the vessel configuration would allow the waste tank directly below the head , a good RV unit would be best of all.
No guest,hassles almost no water use and almost no repairs decade after decade..
Lavac Marine Toilets
www.lavac.com/