My G1 experience and preferred lenses
I would go with the 28. In fact, I did. And shortly after, bought the 45. As you may! Contax Gs and those Zeiss lenses can be addictive. I got my first G1 in 2004, it was GIVEN to me, yes, given, by someone who was bowing out of photography and being generous to friends who shared his love for 'quirky' cameras. Believe it, the G1 is quirky!
I now have the 21mm (a lovely lens, but very little used), 28mm (my favorite), 35mm (a wonderful 'street' lens with very special luminance), 45mm (good to have, used now and then, sharp as new razor blades), and 90mm (almost never). Oh, and FOUR G1 bodies - a few years ago the G market hit rock bottom in Australia and Asia, and I decided to stock up on them, as one expires, if I can have it repaired I will, if not, well, there are three others to grab.
Quirks. The autofocus system can be a b*gger to learn, but once you work it out, it's great. Film rewind is noisy. That fraction of a second gap between pressing the button and hearing the shutter 'tick'. Figuring out (or remembering) how to set ISO and other settings using the damn small buttons on the left side. That's about it, in my experience.
When you've worked out how to use the camera, and have your shooting 'flow' set up, you will probably love it. Last year I carried two G1 bodies with all my lenses (the 21mm and 90mm stayed mostly at my hotel), I walked the entire Bromo Valley in East Java, Indonesia, over four days. Shot 15 rolls of ten year expired Tmax 100. Home processed two months later when I returned to Australia. Exquisite results.
All this to say, Contax Gs can be addictive. I'm often asked why I use the G1 and not the G2. I've tried both. It's because I'm cheap! G1s sold for A$100-$150 a few years ago, compared to A$400+ for G2s. Who needs the better viewfinder? The shutter speed-exposure control dial moves around a lot during shoots if you are not super careful, but a small bit of gaffer's tape quickly fixed the problem.
Whichever lens you buy, I hope you will enjoy it. As I am. My first G1 has been with me for almost 12 years, and is an early model, probably 1994 or 1995. Has never broken down or failed me. With proper care, they are like Sherman tanks.
Enjoy...