If you only had 30 minutes 3 times a week?

For my goals, I would strength train

I would strength train, and then find creative ways to get more walking into my day in short bursts to get some unintentional cardio.

Both.. alernate days. Cardio one. Strength the next..

The one you enjoy the most, because that's the best route to life change that sticks.

Preference being equal, strength training or a mix.

Note that some cardio is more encouraging of strength than others: I mostly row (on water when I can, machine when I must), rarely strength train consistently (even though I think it would be better if I did), and am not completely lacking in muscle, despite being female and pretty old (63).

Cardio because I enjoy it more. I would hate to waste what little time I have on something I don't enjoy.

I'm a runner, so if I had to chose I would run. But maybe you could compromise. How about two days of one and one day of the other and just do your favorite on two of the days?

Could be tricky / unproductive to try and do Cardio in 30mins, if you’re doing a 10min warm up and cool down, possibly doing some stretching too, that only leaves max 10mins of effort level workout. But it depends wholly what level you’re at and what your goals are. Just don’t sacrifice a solid warm up and cooldown just because you’re rushed.

It depends on what your goals are. I'm a cycling enthusiast who lifts primarily for cross training and to help maintain muscle mass while I age. I would likely go with 2 days of cycling and one day full body workout in the weight room. If I was that limited for time, going to the gym wouldn't be a priority because it would take me at least 15 minutes to commute there and back; so in reality I've used up an hour.

One thing I do regularly is get up from my desk every hour to take the scenic route to the bath room and water cooler...I work on the 3rd floor, but I usually use the restroom and break room on the first floor to get more general movement in. I do this regardless of how my exercise is going, but it is particularly helpful on those weeks when I know I'm not going to get my usual time in for exercise.

Another option here would be circuit training which would give you sort of a combo of resistance training and cardio.

I'm just curious though...what do you do that you can't find 30 minutes most days? I'm pretty busy and typically work 10 hours per day including my commute and have two little boys, a wife, and home to take care of and I can usually manage to find the time most days for 30 minutes. When I can't it's usually more of a "I just don't feel like doing it because I'm tired or whatever" kind of thing. My time is pretty limited, so I limit my actual gym time to 2x per week at lunch...the rest of my exercise is just opening up my garage and getting on my bike and hitting the road for whatever amount of time I have available...during the work week that usually amounts to about 30 minutes, sometimes 45. I try to get in longer rides on the weekends.

My 3x per week workouts take a bit longer than 30mins with warm up and stretching, but no more than 45. I do a full body strength routine (Nia Shanks) and then 5-10 minutes of “metabolic conditioning”. It’s quick, fun, makes me feel great, and I’m seeing real progress in my strength and general fitness.
I do stay active on other days, mostly walking the dogs, but I consider that more general life than a workout.

Both! I enjoy cardio, plus hearth health is very important to me. So is strength training for body composition and keeping my strength up.

I would do a 2 mile, 30 minute walking workout that incorporates light handweights, bodyweight or resistance bands for 2 days.

The 3rd day would be pure strength training such as all moderate to heavy weights, TRX or calisthenics. These workouts gives me a slight cardio effect.

Also I would try to find ways to fit in small activities and increase my NEAT throughout the week such as using my mini stair stepper or doing light floor work while watching TV, parking further and walking, taking the stairs more etc. Also there are short 10 minutes workouts I could fit in.

Fitness is a huge priority for me so I would find ways and make it work.

HIIT with weights / plyo. Les Mills have developed GRIT classes in three formats; cardio, plyo and strength. I incorporate one a week into my routine but if you really only have half an hour three times a week then my suggestion would be something like that.

If you want to do it on your own then look at Kayla Itsines Bikini Body guides. I did these workout consistently for about six months (together with other gym) and found them really effective.

For me, I'd doing a 30 minute jog. But for many they enjoy strength training more. I do like @DancingMoosie idea of the 30 minute workout videos that could be both strength and cardio.