Re: yet another annoying cross training q
I think it depends on what your goals are . . .
Are you interested in learning and practicing an artform? How long have you been doing aikido? Is effectiveness a primary concern?
Depending on your goals for training, it may make a lot of sense, as others have noted, to train in an environment where you can get some resistance-based randori/shiai.
A word of caution, though, I don't really recommend trying to learn, wholesale, another martial art if you're just starting in aikido as, initially, the body mechanics and training goals may seem to conflict (not to mention the ukemi can be different enough to make you frustrated AND crap at both if you're just starting out and trying to make sense of it all).
Also, depending on how much time you have to dedicate yourself to training, if you only visit one place once each week, you're not likely to really get anywhere in either system (in terms of getting the transmission, muscle-memory and intangible "stuff" that comes from budo).
Assuming you're convinced you want to do two systems, have time to give both plenty of attention and have a good base in aikido already:
Are you looking to continue to primarily practice kata? Then Danzan Ryu might be a better fit as the schools I've visited typically follow this model of practice more closely than the judo schools I've trained at.
Are you looking for effectiveness as quickly as possible? Good judo players are all-around tough folks. I, personally, think a combination of kata (aikido) and shiai (judo) makes for great well-roundedness in terms of purity of form and the ability to mix-it-up. If you have time for both then that's probably the course I'd take.
Also, my caveat is that I'm writing using a lot of generalities. If we're sticking with the aikido is a path metaphor, though, while I agree there aren't any shortcuts to the destination that practically nobody reaches (YMMV), I don't think there's anything wrong with taking detours to explore different scenario (or even mode of transport), so long as you keep making progress on the path.