If you're not a light packer like butterbarter, one thing you need to consider when getting your luggage is how the bloody thing handles when it's packed and heavy.
I have a samsonite and even when it was 32kg (I was carrying 2 cast iron pots back), it was quite ok to manoeuvre it. Sure, when you have to lift it into the cab, it's still a pain, but when you're wheeling it around, it doesn't feel that much more difficult than when it's like 15kg.
Compare that with another 4 wheel luggage (some japanese name that I couldn't remember) that I have. It's smaller and even when it's lightly packed, it's a lot more difficult to lug around. Gotten to the point where I just use my samsonite - even if i'm only filling up half the suitcase (or less).
And you'd be surprised at how light some of the samsonite hard cases are. It's not much heavier than the canvass ones sometimes - in fact, I think some of the cheaper brands' canvass ones might be heavier if you compare same size. Of cuz it lightens your wallet by a lot more so look for promos if you have the time (the current promo is not that great).