I would always opt for outdoors if the weather’s good. The only workouts I have trouble doing outdoors are threshold (including over/unders) and sweetspot. The terrain around me just didn’t lend itself to those workouts.
If I’ve a SS workout to do I might just swap it for longer Z2 when the weather’s good. For threshold I’ll move it to a different day of the week, where I know the weather might be worse.
Time, weather, and style of riding. It takes me 20+ min of riding to get from my house to clear roads without lights/traffic/bunch of stop signs/etc. I’ll Z2 ride outside if it’s more than 2 hours.
Just hard to be the trainer when facing time constraints. I’m drifting further and further away from being excited by racing and just like being in good bike shape, so outside isn’t as important as it once was. Crashing/hit by car/buzzed by drivers/etc is just a lot to worry about now. That for sure plays a factor too.
Generally only inside if constrained by schedule and work/life circumstances.
Being out in nature and observing and interacting with the world is so much more soul fulfilling to me than being inside. Riding inside gets the workout done, which is satisfying, but lacks any sort of further enrichment. I always feel fantastic after an outdoor ride and happy about whatever I need to do that day.
Sometimes I’ll decide a highly structured workout is better done inside though.
Time, light v dark, weather and purpose are factors determine my ride. I won’t ride alone much in the dark (unless its a commute). I will ride in the dark and wet if I have company but that scares most folk off anyway. Although touch wood nothing has went majorly wrong on a ride, I also don’t want to be stranded 30mins + cycle from home when I don’t have time.
I do all efforts on the trainer. I really enjoy the specificity and control. Plus I’ve got a great set up now with entertainment and fan etc.
I can get a five hour ride on the trainer during the preschool day significantly more easily than outdoor as I can be on the bike within 10min of drop off and ready to head to pick up within 10min of getting off.
I ride outside if it’s fine weather, and only after my interval session has been completed. It’s all MTB on the trails so it’s also really important and I can get good endurance out of riding fatigued.
I find it easier to mix the two during Build than Base (1.5hr VO2/Threshold session + 2-3hr MTB vs 2-3hr SS + 1-2hr endurance)