The elbow is actually for easier rubber banding. It really doesn’t effect its height, but does make it heavier. I really depends on your gear ratios and how heavy is the weight that you are lifting
The elbow thing (also called a 4bar) seems to be the strongest from my testing. Also it seems to be the most equal while lifting using only one motor (meaning that one arm isnt higher than another)
The four bar style arm is great for banding and is much better than direct in my opinion. However, it makes the arm a bit heavier. The lever style arm allows the arm to be really light and is probably the best choice. The direct arm is the worst of the three. Additionally, bracing the arm in the back can be very good because it allows you to lift the arm without raising the tray.