Other possibilities
While the previously mentioned boats are fine I noticed that you want a 16' to 20' boat. This leads to a set of questions.Are you thinking that you might like to spend a night aboard or are you thinking that just a daysailer without a cabin of any sort is about right? I see you asking about a daysailer so think you are looking for a more open boat. Do you want a minimalist version? That is, do you mind getting wet or are you inclined to a little more comfort? There are storage questions as well. Did you set the 16' - 20' limit based on your available space or was handling your critieria? Also, even though this may be your first boat are you somewhat experienced or are you inexperienced? There are lots of questions that could be important.My suggestion here would be that if you are looking for simplicity of controls and a little comfort to along with improving your skills you might look at something like a Montgomery 17' or 19'. These are tough little boats that will be fairly stable, are easy to operate for the beginner but also capable of traversing relatively long distances. They are dry for this size boat and have a cabin for stay aboard activities. Another in this class of boats might be the West Wight Potter. Similar characteristics and capabilities. Same with the smaller Compac. Each delivers on the promise of safe secure sailing with a twinge of adventure and far away places because they are closer to sailing a larger cruising boat.If you are more intent on just zipping around the lake or bay, don't mind getting a little wet from time to time, won't have small kids on board in the early stages of learning and such like considerations you might like an old M-Scow or racier large sail area skimmer. You will get wet, you will smile a lot and you will learn how to keep it on it's feet. Stability is not a strong point for this sort of boat but, frankly, the exhileration factor (that is, the near fear factor) is wonderful. If your reaction time is a bit slower - like mine is these days - you may end up wetter more of the time than you end up drier in the learning process.A lot of the choices you may have also depend on how far afield you are willing to go to find the right boat. You may or may not have the "right" boat available in your local area. There are more Montgomery 17/19's in the west than the east I would guess and more Compacs in the eastern portion of the country. So, availability of the type of boat you want may have you looking further away than you might like.In any case, enjoy looking for the boat and then when you find it sail the daylights out of it until you understand how to make it move exactly how YOU want it to.Best;Chris