I have used both systems. My current company does not use per diem. I wish they did, because I often don't eat much so I could pocket alot of extra money. It depends on your eating habits. If you like to eat alot of expensive meals then perdiem would be a bad option. If you live off free hotel breakfast and subway, then you'll make money on the perdiem system.
Plus the extra per diem can be used for entertainment on the road, ie... movies, golf, museums.....plenty of other things to do with it. Good luck trying to expense these things if you lose the perdiem system.
I know this sounds childish, but some of the pilots at my company who think they are making a point, purposely buy alot of extra food and desserts that they don't eat. They often give it to the bums out on the street. Good cause...... but for the wrong reasons. These pilots think by spending extra on the expense report, the company will switch to per diem and save money. I guess they think they are sticking it to the man. I don't think this tactic works because they've been doing this for years and no mention from management about changes has ever come about.