I'm one of the poor souls that doesn't live in sunny California , so I use both during the winter (although this is my first "offseason"). If it is over 40 and there's no snow on the roads, I'll be outside.

On the trainer, I've been using the "Spinnervals" DVD's. Pretty good workout for me.

I've also been doing spin classes. They are also a good workout, but they seem more like the stair-climber machine set to music. That may just be the class that I'm in -- it seems 80% of it is out of the saddle, which is good for me, but I don't think that the "bouncing" to music is particularly efficient cycling practice.

All said, either one is better than nothing...