I have done judo for about 7 years. To think about it now, all what I got from it is bad knees and a lot, really lot of stress. Performance was crucial, and since I was not particularly good at competitions, I was always looked down at by my dojo mates. Training was fun though, and I enjoyed it, especially during periods when there were no imminent championships and atmosphere was relaxed.
Technically, I believe that judo and aikido could not be more different because they are based on completely different concepts. My previous judo experience has helped me a lot in my aikido progression in the beginning, but it soon became a hindrance when I reached somewhat a higher level.
I wouldn't recommend doing both though. The natural progression would be to start in judo and then move to aikido. Doing the opposite doesn't seem very logical to me.