Id rather set up in the plains than the swamp, at least i can grow biome-specific stuff in the plains and im not constantly wet, but it also heavily depends on where you actually are in progression. If you are just now getting into a swamp and considering making a swamp mining base or something then there are a few better ways to go about it (assuming those options are available, some land spawns just hate you). If you just want a safe little camp then the tops of crypts or in the giant trees are decent places (i recommend a portal, yeah ores cant pass through but boats and swamps dont always get along well thanks to leeches).

If you want an actual outpost/base, try to find a meadows or at least a black forest adjacent to this swamp you are after instead and set up there instead. If this continent is basically just that swamp and the plains and you are indeed just getting into swamp, well for one you might want to see if there are easier options for you but otherwise, you can indeed set up in a swamp that borders a plains and still be relatively safe. It can be dangerous, but you can help yourself reduce those risks to. It's just somewhat labor intensive sometimes since it can also include using the hoe to level pathways around the swamp or tree climbing for the purpose of building a base in one of the indestructible trees since the only thing to really bother you up there are fliers and archers, if they even realize you exist. Plus you might be a bit vulnerable during these renovations since you won't have things set up just yet and may be distracted with your tasks. So yeah, it can be dangerous, but it also can be done if you want to. Just uh, mind the lox. Had a herd come over a cliff into a swamp i had set up in before and they were the biggest problem in that swamp for the next in game month until they finally all got killed off. Also, deathsquitos, it wouldnt hurt to keep a shield on your hotbar, bonus that the serpent shield is extra resistant to pierce and obtainable around swamp tier.