11.12 on intermediate, another 11 and several 12s today. Here's to hoping for a 10 or even a 9...

For intermediate the fastest strategy is to not use flags and solve like this:

Solve the outer edges of the board going around in a circle. Use guessing if neccessary. Stick to the same starting point and the same assumptions when guessing in order to solve this without slowing down to think. You are going to lose a lot if not most games this way but if you're trying to be as fast as possible it's worth it. The games you lose this way will be lost early and not cost too much time overall. The games you get to continue past this starting phase will usually be much easier and quicker to complete.

Then solve column by column. It's up to you whether you only use logic for this or make occasional guesses to save a bit of time. The more guesses you make the fewer boards you will win but it might be worth it after coming within a second of your record for the twentieth time.

For genius I usually just look for a solvable outer edge. Some days I only play boards with a solvable top or bottom row and some other days I try to get a board started by guessing one or two safe squares on an outer edge. I don't have any specific strategy for genius beyond the start of the board except that occasionally I remember to not use flags during the last 5-10 seconds of the game to hopefully save a second or two.

Sorry for using "secret language": my mobile phone only speaks German and chances amost every word I write...