I'm a
finance attorney in NYC with a lot of friends in ibanking. My perception is that ibanking gets steadily better while Biglaw gets steadily worse. (Anonymous to not out myself through previous posts).
Working ridiculous, unhealthy hours is generally the norm in ibanking for your first 2-4 years, and in those years you work significantly more than your biglaw counterparts. However, at this time, you're about 22-25 years old, don't have a lot of commitments, and honestly - it's kind of fun. There's a good amount of partying/comradery within these junior ranks.
Most of my friends who started off in ibanking switched to buy side within their first two years and their hours vary a ton based on the PE firm they're with. Those still in iBanking are VPs and their hours are significantly better. They seem to work about 50-60 hours a week and have a mini-army of juniors to do the grunt work. Of course, shit happens and they do have weekends blown up and do work long hours when a deal is closing.
In Biglaw, your hours generally get worse and worse the more senior you get. You also start later in life due to law school and your hours ramp up right as you may get married/start to have children (literally the opposite of ibanking where your work hours get better as your personal life commitments become more time-consuming).
Basically, I believe an ibanking analyst works more than a junior associate. However, I think a midlevel/senior associate works more than an ibanking associate/VP. I don't know any MDs on a personal level yet, so I can't speak to their hours. But, partners - especially junior partners - work a metric shit ton. I came in thinking I was going to gun for partnership for sure, but seeing how much my junior partner works - just don't think it's worth it unless you really really love this job.
FWIW, if I could go back, I would've gone down the ibanking path. Less schooling, less debt, more money, better exit opportunities.