Thanks! I see Vega being the key to making big gains on calls. In Nov imp vol surged and I should have sold calls heavily (both covered calls and sell to close long calls) as option prices soared. 

I don't search for a delta when choosing.  When I sell ATM for 7dte, then delta is about .5. When I sell OTM at 35 DTE then delta is probably between .1 and .3 (0.16 is 1 standard deviation).

When I'm buying calls it depends on what strategy I'm using. When doing pmcc then the long calls should be above .7. If I'm just speculating on ngu then I go out beyond 180 DTE in most cases and buy the top of the option chain, the smallest delta (cheapest per $).

Buying calls under 90 DTE is degen shit IMO even though I will sometimes play around with a position size that can't hurt me.