If you're deciding solely between those two models of boats then I'd definitely go bigger and get the 232 Gulfstream. The 218 Adventure looks like a nice boat but I'm honestly not a huge fan of the Euro style transom. I like the 232 Gulfstream, as well as the 228 Seafarer, in that it has a transom bracket that encloses the stern of the boat. The 218 Adventure feels a bit too "open" on the sides for me, and the motorwell looks like it takes up a good amount of space that could be used for fishing, storage, extra persons on board and so forth. If you do get a 232 Gulfstream then I think it would be silly to get one without twin motors on it as that's one of the biggest reasons why people get that boat in the first place, so they can have twin motors on them. I think You could honestly also go with a third option for boat models, and that would be the 228 Seafarer. It took me just over a year to find my boat but when I was looking, I saw a lot of 208 Adventure's as well as 232 Gulfstream's pop up for sale and briefly "considered" looking at both of those models. The 232 Gulfstream is a pretty big boat and for fishing relatively protected waters out here in the Puget Sound, it was definitely a much bigger boat than I needed. The other things I didn't like about it were the bunkbed style cabin as well as the step on the deck.
My parents are in their mid 70's now and I didn't want them slipping or tripping while out on the boat, which my 228 Seafarer has an all level floor comparatively. And as mentioned, the bunkbed style of cabin that the 232 Gulfstream has does absolutely nothing for me. So, it wasn't long before I crossed that model off the list, and the 208 Adventure I wasn't really a fan of with the open style of transom as I moor my boat on a mooring buoy all summer, sometimes unattended, and to where I didn't want to have a problem. The 228 Seafarer is just about perfect for what I use the boat for, which is trolling for salmon, crabbing, shrimping and cruising. She'll do close to 45 mph @ WOT, does considerably better on fuel than a larger boat with twin motors will and she didn't break the bank when purchasing her. If you're considering the 218 Adventure, I wouldn't immediately dismiss the 228 Seafarer, especially since they made the model up until about 2021 or so. Sure, there are a few things I wish were somewhat different on the boat, like the cockpit space between the seats is a bit tight if you're a bigger guy. But it's nothing that can't be remedied by simply cutting off the inside armrests on the seats to give you considerably more room. The walkaround portion can be a bit tight if you walk with your feet point towards the inside of the boat, though if you walk with them pointed forward or backwards then you get a bit more space to walk. I'm also thinking that a used 228 Seafarer/232 Gulfstream is going to be less money than a brand new 218 Adventure. Just my thoughts of course, either way good luck with your search and I'd try to step foot on both boats, figure out whether you want a boat with twin motors or just a single, etc.