Short story:
I reserved a Honda Tornado through them which wasn't ready the day of and got a few different answers on why. I was told the bike would be there by 3:30, came back at 5:00 and it still wasn't there with no ETA. Seemed very informal and shady, decided to cancel the reservation and enjoyed Guatemala without the motorbike.

Longer version:
I had reserved a Honda Tornado through Simoon Rentals vai their website and a couple emails later I had it reserved for 8 days to tour the country. I arrived the day before and was surprised because the location is a literally a flower shop. I introduced myself and asked a young girl working in front about the bike, she made a call to Fredy who I had reserved the bike with by email, and she said, yeah, we'll have the bike for you tomorrow. I arrived the next day at 11am, she gave Fredy a call and said the bike wasn't ready, it needed its battery changed in Guatemala city and that it wouldn't be ready until 3:30. My girlfriend and I decided to take our time and we showed up at 5:00. The bike wasn't there and the guy I had spoken with to come back at 3:30/4ish had said it needed some more work done due to it's previous renter. I asked what the ETA was and he didn't know but he called and said it would be there that evening. We thought about it for about 20 minutes and we decided to tell them no thanks on the reservation and enjoyed Guatemala via bus.

My thoughts: Although I would have loved to tour the country on the Honda I have no regrets. First, as a matter of principal, it seemed like such a low-concern on their end until I said the deals off. I was upset the second time coming back to hear that the bike wasn't there but what made me really decide to go without the bike was that they were calling the guy who had the bike only after I asked what the ETA was, seemed shady. I had planned to pick the bike up that morning or afternoon and ride to Panajachel, but ended up spending another day in Panajachel. Plus the changing story made me question what kind of condition the bike may be in. I understand my situation may be isolated but just wanted to share my experience and thoughts. I've seen motomundo post on this forum. I would go with them or CAtours any given day before returning to Simoon.

Sorry to hear about your bad experience .

IMO the best option for renting a bike in good condition in Antigua is definitely this place Motorcycle Tours in Guatemala | MAG Tours