Well if mental health is something to go by.
It seems HIIT and weights is best.
Long exercise sessions are almost as bad as not exercising.
The best amount of exercise is between 3-7 hours per week.
Joint health is about form, if you are concerned about joints, row or bike instead of jog. Use machines instead of bench press.
I know this is an old post, but the
ignorance - it hurts!
Swimming is easiest on your joints in regards to impact, but rotating through different activities is also effective since what you're really trying to achieve - in the long run - is a minimization of repetitive motion. Cycling or rowing obviously won't do this, but rotating through different activities might. Machines like a Machine Press and especially a Smith Machine (for squats) will injure your joints more than free weights will by confining movement to a generic, predetermined path that is unnatural and not ideal for most people. Use a free weight (dumbell, barbell, or kettlebell) that you can handle safely, be mindful of what you are doing (Mindful = attentive,in the meditative/zen way) control the weight at all times (even olympic lifting involves precise control), and move through your natural, full range of motion which is specific to your own body.
Once an acceptable level of fitness is achieved, moderation in all things is probably the best long-term approach, but increasing intensity and/or duration of exercise and manipulating rest periods is probably necessary to reach that "acceptable" level of fitness .
