For me? Gotta be maintenance! - I've lost & gained so much weight in the past 20 years... ranging from 126 - 192. I've done tons of diets, some sane ones (South Beach, Medifast, etc) and some really crazy ones (eat dinner in the morning & breakfast at night!) ... and I've lost 10, 20, 30, even 40 pounds... Keep it off for about 6-8 months, and then "something" happens...
*got hurt & couldn't exercise one time (out of the gym for 12 weeks & POOF! - back to bad eating habits...)
*one time I got severely sick and the medicine I took made me blow up like a balloon... so what'd I do? Ate. (Seemed logical at the time, duh) ....
*the last time I was happily rolling along on MediFast, lost 20 pounds, felt good & was doing the diet just fine... WHEN IT HIT... my husband lost his job in the bad economy time, and we could not afford the MediFast anymore.
So yeah, I'll have to go with MAINTENANCE being the hardest for me!