I really should pick up a ADC display at some point. They are really beautiful and would love to have one to go with my MDD on my second desk as opposed to my generic Dell monitor.
Not only are they a perfect match for G4 era Macs, but they are also a great quality LCD display and very convenient to use.
I've-at one point-owned all the flat panels except for the 15". I've also never the 17" CRT, which I'd actually like to find just for completeness sake.
If you're looking for a Cinema display(widescreen), I'd steer you toward a 20" for a good combination of size and appearance. I had one for about a day, although I returned it(fortunately, I bought it at a B&M store that accepted returns on electronics) due to several severe pressure marks on the screen that I decided were unacceptable for the $40 I paid for the display.
The 22" is older and lower resolution than the 20"(although the difference is not huge). To my knowledge, it's the only flat panel ADC display with physical buttons-it has three located along the bottom right edge of the screen-one for power and two for brightness up/down. All the other flat panels use capacitive buttons, with one on the right for power and one on the left that brings up the display preferences pane for you to adjust brightness. The other thing I'll mention is that my 22" has a noticeable pink cast along the top and bottom edge. It's worse when first turned on, but doesn't completely disappear. I don't know if this is true of all of them.
The 23" is the king of the bunch, and I love mine dearly.
The 17" Studios(studio displays are 4:3) are a nice and convenient size, and are a very high quality display.
If possible, I'd strongly recommend buying in person on Craigslist or likewise. Many folks don't know how to pack these properly, and that's how a lot of the acrylic feet get broken.
When I bought my 23"(the only one I've bought anywhere other than locally), the seller was nice enough to pack it as per my request and removed the foot before shipping. If you do buy one on Ebay or likewise, be sure to request this-preferably before buying. Mine actually came in the box for the Thunderbolt display that evidently had been bought to replace it(the TB display box showed Yosemite, so it was a relatively recent purchase). I actually think I got a decent deal on it-I paid a little under $100 including shipping, and got an A1006(ADC-DVI adapter) with it.
If nothing else, it's fun to hit the power button on the front of the display and have the whole computer power up

. Unfortunately, this doesn't work through an A1006, nor does it work with the 9600XT in my Quicksilver(which I had to hack to get it support an ADC display in that computer).