Spinning vs city bike riding to keep tone
I'd say riding outside is always better than a spin class or turbo-time. I ride a hilly commute to work throughout the winter 10x 30mins each way, but do intervals too - and ride fixed gear for extra effort. Commuting through winter gets a bad rap (depending on where you live). Sometimes, here in the UK, the weather can be pretty crap, but you do get some absolutely wonderful mornings. Better a bad journey on the bike than a good one in the car.

I'm much happier out in the real world than on Zwift or in a class - although there's certainly benefit to those. If you think that's the most realistic option for then do that. I have no car, so I have no choice. With that being said, it does keep me in good shape for the season.

TL;DR: Commute. Makes you fitter, stronger and more road-aware ready for the season.