It really depends on your goals. I find that if I skip one of the conferences that I regularly attend, I miss a lot of emerging technology. I never go to conferences that don't have a vendor show tied to them. I always get a lot more from looking at the stuff that people want to show off than I do from most of the presentations.
Your post sounds like you are a recent grad. For you, the presentations might be fresh and new and amazingly worthwhile. I remember when I felt that way and I got a lot out of them. After a decade or so the bloom goes off that particular rose and the show part of the conference becomes my focus.
If you are just starting out, I probably would recommend one of the big shows (like the ASME World Conference or the SPE Annual Technical Conference and Exposition if you are in Oil & Gas, maybe Offshore Technical Conference if you work offshore) even if you have to take vacation and pay the T&E yourself. Actively look for people to BS with (networking is prime benefit of these things), give away a lot of business cards, spend time in the show. I always find that thinking about a particular problem in my job and trying to find a gadget in the show to solve that problem helps give the show a purpose in my mind and makes it more fun.
David