Both are great boats especially since they have wing seats. The wings really make a difference in comfort and provide a huge "footprint" for everyone. My knees don't like to crawl around the tramp.
I owned my 21 SE since it was brand new in '89 and have sailed with my buddy on his 18 SX for many years, so I have decades of comparable sailing experience on both boats.
The 18SX is considerably lighter and easier to move around on cattraxs, but where we sails ,we don't really use them. We launch our boats from our trailers right off the beach and retrieve our boats the same way (water to trailer). I don't even get my axle wet just the tires. We both use the trailer winch to haul the boats on to the trailer with similar effort.
Having the boat at the beach with the mast up is a real benefit and a luxury I don't have. I choice to trailer my boat wide at 9' 7" (trailer is 10' 3 1/2" wide including the guide rollers) since 1990 and it gets a little difficult if traffic is heavy or mailboxes stick out my the road. You get use to it. I just returned from a 2320 mile trip to southwest Florida pulling my wide boat....
thank god for beer.........and being a fearless man...
I use to believe that I needed crew to go sailing so I picked up a couple of nice 16' Hobie's "for my kids"? Who am I fooling.......
Than one News Years Day, I decided to revisit the notion that I needed crew and started to solo sail my 21SE that spring. I found it to be very stable and enjoyable without depending on anyone else, except someone to help raise my mast. At Paynetown State Park where I sail,a cold beer will get help every time...problem solved.
I solo in 10 to 15 mph wind ....only
10 to 20 knots and you need crew.
Since you will have to haul your next boat on cattraxs to the beach without much help go for the 18SX Or get a second set of cattraxs for better weight distribute and bring more crew and get the 21SE.
Me, I would buy both boats and than pick and choice depending on conditions....
Come on over to Southern Indiana this spring and take mine for a spin around the lake...bring beer.