Which diet plan

[Sunnydaysarethebestdays]

Please can someone explain the difference between all of the MM Fast plans?
ive tried various diets in the past but not stuck to any. Need to loose about 3 stone but I’m more import improve my health.
im confused by Fast 800, 5:2, 16:8 and blood sugar diet.
which the most effective for a newbie?

Dp is using an app called Simple he tracks his intake, measurements, etc.
He's currently doing an OMAD plan.
2 liters of green tea-2liters of water and one meal a day. With the odd cheat once a week or so.
He's gone from 191lbs to 181lbs in a month-his target is around 165-169lbs.
He's encouraged me to do it, but I'm not sure I'm disciplined enough.