what to expect during pledging?

Regardless of how bad it is it's better than being a gdi

All houses: Working parties on weekends until 3am or so, cleaning the house, mandatory study tables, keep your grades up.

Specific to lower tier houses (my experience): just a lot of time commitment, more leniency there, punishment if you mess things up. Its more of a mind game. Easy tasks but they give you way too many, and when you don't complete them all, you get yelled at for it. I got 8 hours of sleep a night but i didn't have class till 11am or 1pm depending on the day. You get to know brothers a lot more and become their friend. They treat you nicely.

Specific to upper tier houses (friends experience): expected to be at the house until 4am multiple nights per week, lots of workouts, forced to drink, ridiculous/embarrassing tasks, occasionally something dangerous. Some brothers treat you like crap and you don't get to know them as well because of it.

If you get through pledgeship, you will have fun and attend parties and meet girls and make bonds with people for life, regardless of which fraternity it is. One big difference is you will pair with more attractive girls when you join the higher tier fraternity. Join the fraternity you click with the guys the most with.

There are some Fraternities that have sober pledge-ships, but from what I have seen they all demand a lot of time and late nights.

There is also a lot of "you guys suck and are the worst pledge class ever" kinda of talk. If you can learn to not take it too seriously you will be fine.