I learned on an O'Day Widgeon 13; it was a good boat to learn on because it had most of the controls common to all sloops (2 halyards, 2 sheets, outhaul, downhaul) but I wouldn't recommend buying one because you can't really bring much with you. A 13' boat will be too small by the time you've learned how to sail it.
I'd recommend a 15-16 centerboard sloop. I'm thinking of the O'Day daysailer, but that's just the one that I'm familiar with. Very easy to tow, set up, launch & retrieve. Plus it is small enough to move with a 6' paddle. But it is big enough that a fairly skilled skipper could take a guest or two out for a day sail and return them dry (9 times out of 10
Also 2 people that really like to sail and aren't afraid to tumble into the water can sail the ever lovin' snot out of it! You could sail it for years and it would still be fun. I still miss my Luger 16