The 66 is a cooler gun, discontinued, less common and worth more etc.
I don't very much like the glock 23 only because of the caliber. I would certainly make the trade. You can always find another glock. I think the recoil for a 23 is esp snappy for a gun which is designed for SD. For that size glock, 9mm is the way to go, IMO.
I have a 66 no dash and a glock 19 3rd, and while I love that model glock, I would probably do the trade even then if I were you. I need my glock 9mm however for carry, so I'd be less likely to do it but for you who traded to get the glock, and doesn't care for it, you will probably like the 66 much better.
Also, the 2nd gen glock does not have the accessory rail, so if you hold onto it, its a less desirable glock to others. In other words, between the size, cal (9mm is better to have and appeals to more people) and age, it wouldn't be the easiest to unload BUT it is still a glock.
One last thing, I currently have seven 357 mags, a Python and 6 S&W 357s. My 66 is my favorite out of them all. Between the feel, the lighter weight, exc trigger, adjustable sights, SS, etc, you can't really ask for anything more. Its all you need and nothing that you don't.