I worked in a small-town McD when I was in college, then again when I moved to the city without a $ to my name. A lot depends on the atmosphere in the restaurant, but you can affect that yourself to some degree - cheerfulness can be contagious.
The small-town store was good - it was very hard work and I went home every day tired & with sore feet, but I loved interacting with customers and I thrive on working hard & being active - I can't stand just sitting around doing nothing, so it was good for me - you have to clean when you're not helping customers. I preferred the counter & drive-through to the grill, but I'm a klutz and kept burning myself.
A lot of times if you're very sweet to the grouchy customers they'll turn around & apologize for being grouchy, too. I love that.
I was promoted to mgr. pretty quickly, so that was nice, too.
I didn't like the second store in the city, though. Most of my coworkers did as little work as possible, and were very sloppy and dirty. Even the store mgr. was lazy! I worked there 2 days before I found a different job. Try visiting the restaurant where you're thinking of working and observe the employees - you should get a feel for the attitude of the place pretty quickly. Is the store clean?
Are the employees grumbling under their breath, or even out loud? If it's bad, try a different restaurant.
The nice thing about McD is that they don't hold it against you for leaving quickly...and it doesn't look bad on a resume if you don't work there long. People understand. When times are tough, you have to take what work you can find.