im looking at what I want my timetable to look like, and I was wondering, is it better to have three 40 minute classes of one course a week, or is it better to have one 3 hour class of one course a week?

If you're talking about nightclasses, avoid them if at all possble. I have found them to be a huge pain in the ass. If you have an 8:30 class the following morning, they realy prohibit you from getting enough sleep.

I hardly attended night class in first year because your days are soo long. However, my summer courses are night classes so I'm getting used to taking classes at night which is why I'm taking it next year. Also, make sure you don't have morning classes the day of and the day after your night class.

Three hours of the same class can be a drag, especially if they don't give you any breaks. I'd recommend spreading it over the week. Also note: missing 1 out of 3 classes in the week isn't bad... but missing a single 3 hour class can really hurt you when it comes study time and you're missing a chunk of lecture material. It can happen... you're sick one day or need to finish up a project and can't attend a class, etc. If you are going with the 3 hour, make sure to have a good friend in the class with you (or make a new friend!) who can be there to help you with notes if you're away

depends on the type of person you are. Here are some factors to consider:

Are you a morning or night person?
Most 2+ hour courses are at night, I wouldn't take them because I don't like being cold and not having transportation arrive promptly. I also get sleepy around 5-7, but cannot fall asleep until after 2 a.m. if I miss that 2 hour time bridge.

Do you get bored easily?
3 hours straight is not a good idea for someone that has difficulties staying wide awake, or focusing in on the material. The 45 min classes I like because they are snappy and take just enough of my time to teach me something, without making me wonder wtf I am there (sometimes this still happens, depending on the lecturer and subject).

How well do you use time?

I don't like to be in a rush and am not to keen on getting everything done and having the rest of the day to myself. This is why I prefer to have gaps in my day for tea, relaxation, exercise, food, etc. As such, I tend to group my lectures and tutorials. If I have 2 back-to-back or fairly close by, I will take a 45 min break after them. If I have 3-4 with some back-to-bac and others withIN little gaps of free time, I will designate 2-3.5 hours to refresh myself.

Then again, I highly doubt she would have ALL night classes. Having one night class a week isn't brutal. Just make sure you'd be interested in the course. And take a nap before lecture. There are more cons about night classes than pros but sometimes you just have to take a night class because it's the only available time. Night classes aren't the best idea but it's not the end of the world either.

Although it is unlikley, you can have up to four night classes in a term.

I know someone who did that. However, it's because she was working full time. But she hated that schedule.