We've snorkeled a lot on the Big Island and
Castaway Cay. We bought our equipment and bring it with us. Here are the things we consider:

We must have a completely dry snorkel (dry top isn't good enough). This allows us to dive down without getting a mouthful of air. I believe you can learn a technique to prevent this, but we've never needed to with the dry snorkels. As soon as the top of the snorkel is submerged because you dove down, a wave came over you, or you tilted your head back; a stopper prevents water from entering the snorkel. We've bought several different kinds and they've been awesome. I ordered some new ones from 101snorkel recently that look good for less than $15.

For a mask we just like the ones that have a q-strap that adjust in the back. These are hard to find. We've had pretty good luck with most masks we've tried.

For fins, we bought the type that allow you to wear a dive boot. They have adjustable straps behind the heel that hold the fin on. This allows us to walk along the sharp lava wearing the dive boots until we get into the water where we can get our fins on. The fins are worn over the dive boots. I don't know how many times we've watched people stub their toes and trip over sharp rocks as they've tried to get into the water on Big Island beaches (Kahalu'u especially). If I was going to do all sandy, beach entries; I would get full-footed fins that slip on and don't have straps. We bring our old standby pull-on fins when we go on a
Disney cruise for Castaway Cay.

We use de-fogger all the time. We don't head to the beach without it. I think the kind we've tried recently is the Seadog Gold??? It was fine.
A couple other recommendations:

Try your new equipment in your local pool before you cruise. This allows you to adjust the equipment before you get to the beach. There is too much going on the first time you snorkel in the ocean to have to worry about your equipment.

Never touch any of the coral. We see so many people standing on the "rocks" when they snorkel while they adjust their equipment. These rocks are living coral communities that support a myriad of sea life. If your equipment needs adjustment, please find a sandy spot to stand. The coral heads at Kahalu'u and Haunama Bay are totally bare on top from people standing on them. So sad. The lifeguards at Castaway Cay are always asking the snorkelers to not stand on the sunken objects that are doing their best to support new coral communities. It will never happen if they are being stepped on all the time.

Wear a rashguard or t-shirt if you snorkel for any amount of time. It takes a short time to get burned when you are snorkeling. Time gets away from you while you chase fish and search for treasure and you can fry out there. Sunscreen on exposed skin is also a must. We've found gel type sunscreens to work best (BullFrog QuikGel specifically).

For all of the reasons above, we would never rent a mask or snorkel while traveling. We schlep one large suitcase with four sets of snorkel gear whenever we travel to Hawaii or a Disney cruise.

We figure at $25 to rent gear for a day at Castaway Cay or a week in Hawaii, our gear has quickly paid for itself.

Don't try to walk on the beach while you are wearing your fins. We wait until we get waist deep and slip them on. If you must walk with your fins, it is easiest to walk backwards.
Sorry for being so preachy....hopefully you can find some snippets of info that will help you in your search for snorkel gear.