I own several of both, and they are both good routers. there may be better, newer designs out there, but I have never bought or owned any other router, (other than a seventies vintage Crapsman, that deserved the name). Both have the same collets, which if you look online you can find in 1/4, 3/8, and 1/2-inch, as well as 6, 8, 10, and 12-mm. This makes them extremely versatile, and gives you the ability to buy various diameters of end mills off eBay, and the 8-mm shank bits that work with the Leigh jig, and chuck the up securely, without using adapter sleeves, which I personally don't like.
The 890 has a bit more power, and works better in a router table due to the built in adjustment system. It is also a lot newer design, with the same motor diameter as the 690.
In the 690, be sure to get the variable speed motor. If you decide to go that way.
The plunge base for the 690 has an issue with not wanting to release the motor. This is easily solved by drilling two small holes in the base next to the screw you tighten to lock the motor in the base, so you can get a small punch onto the top of the plate to tap it loose.
The 890 motor will work in the 690 bases if you remove the gear rack that is part of the height adjustment with the 890 base. So, you can buy the 690 bases for use on frequently used jigs.
Personally if I was buying one or the other I'd go with the 890. It costs a bit more, but is a newer design, with more power, and a slightly better variable speed control with soft start.