I’ve had mild success with MILD (ha ha - get it? yeah, it sucks. what do you want from me?), so I may as well share my experince.
For me, I think the best mantra is the one you make yourself. You’ll find it easier to remember, and recongnise it easier and stuff.
But I have one question - with MILD, are you just meant to suddenly remember that your dreaming, or do you just suddenly just remember to take a RC? Cos usually for me it’s the later (not always mind).
Oh, and for anyone interessted, I try and repeat my mantra till If all asleep. I find it easy enough, as as soon as I lay down for sleep now, I automatically start saying it in my head. Sometimes I just can’t be bothered (hard day or whatever), but I generally try to keep at it for at least half an hour.