Just get one of each... That is what I did.
My wife and I weigh about the same as you do.
I have the 16 for racing..
The class is much stronger and it is very easy to find someone to casually race against.
It is a bit simpler to trailer sail..
Something about the wilder ride is very fun.. the weight sensitivity, ability to pitchpole with relative ease... All this makes the 16 exciting and fun to handle.
It is easy to rig and easy to sail.. easier to manage on the beach....
I don't see any real negatives to owning the 16.
With the 18..
It is smooth on the water.. The little bit of extra weight combined with the length make the boat ride like a Cadillac compared to a 16.
The boards let the boat point MUCH higher into the wind and are not really all that much of a hassle.. and look great in photos when flying a hull...
The 18 is more tune-able.. More strings to play with allowing finer control of the boat. For a new sailor this could be a bit overwhelming (if you allow it to be) but once you learn the ropes this allows you to be able to depower or power up the boat to a much greater extent than the 16 making the boat easier to handle in almost any condition..
The roller furling jib... Adds complication to trailering.. (not much just a little) but if you are keeping an 18 on the beach... Seriously.. hoist the main and you are on the water in 5 minutes... Hit the beach for lunch... Furl the jib... wind picks up and things are way out of control.. furl it..
At 225lbs.. I bring something to help me 'right' the 18 should I dump it... But if I am just out playing solo... The 18 is an easier boat to handle. It is easier to kick out on the trapeze.. and isn't as weight sensitive... Meaning unlike the 16 I can just kick out on the wire and not worry about flipping the boat or dumping myself in the lake on the wrong side.... Now.. all that is much of what makes a 16 fun.. but without all the action it means you can settle down and really sail an 18 HARD... Stick the bows down close to the water and let it rip without the same level of concern the boat might decide you need to go swimming.. (talking about 15+mph of wind)
If you think you might have three adults going sailing regular.. the 16 will do it.. The 18 will do it better.. The 16 will 'handle' plenty of weight but it slows down quicker with more weight.. and for whatever reason.. There just seems to be more room on an 18 for extra people...
But.... this also means if you have a 16... people just have to take turns.. This isn't always a bad thing.
You can't go wrong with either boat... I sail my 16 more simply because I enjoyed the regattas, and the 16 fleet is much larger and sailing with/against a matched boat is very fun... The 18 is just a really cool durable old boat... I love it...
Get one of each.