Always look at: winrate and time. You will have to find out yourself what works for you best. If your highest $/hour are in HU sng's then play those.

Also look at winrate per open tables. For example: You might be let's say winning 1 out of 4 STTs when playing only 1 at the time, winning 1 out of 5 when playing 4 of them at the same time. And winning only 1 out of 16 when 8 tabling. So in this case playing 4 is the best choice (since your $/hour is bigger than playing only 1, even though you have a better winrate in playing only 1).