Choose cardio by specificity, recoverability and preference.
Combining Cardio with Strength Workouts is not automatically easier with one “best” machine. The right mode is the one that develops the aerobic quality you want while fitting your joints, skill level, available equipment and lower-body recovery.
Walking and incline walking
Walking is accessible, easy to dose, and usually simple to recover from. It can raise weekly activity without demanding another technical workout, making it a useful baseline before adding harder conditioning.
Cycling and other low-impact options
Cycling can deliver substantial aerobic work with relatively low impact. It is convenient when a trainee wants conditioning without adding more running contacts. If you use heart rate to organize intensity, compare the Heart Rate Reserve Calculator with the Training Heart Rate Zones Calculator.
Running
Running is specific for runners, field athletes and anyone who enjoys it, but harder running also adds impact and local muscular stress. When Combining Cardio with Strength Workouts for a running goal, the answer is not to avoid running; it is to keep the key runs high quality and place heavy leg work so that neither session is repeatedly compromised. The Running Pace Calculator can help translate distance and time into pace.
Intervals
Intervals are useful when they match the goal, but they count as hard training. If your week already includes demanding lower-body lifting, frequent all-out intervals can create a recovery problem even when total cardio minutes look modest. Reserve the hardest conditioning for a reason.