Mid-range mini U-locks are much lighter weight than the locks you mention and still give you a good amount of security against non-pro thieves. I use an OnGuard Bulldog Mini, but Kryptonite Series 2 is similar.

If you're locking up your bike for an extended period of time (at home or at work or at school), think about leaving a heavy duty lock at your destination so you don't have to carry it around with you.