Olympic weight set or dumbells?

Both are good, depends on what your goals are. Generally a barbell setup is going to offer more options.

OLY all the way, much bigger capacity when you get stronger and more options

You'll find you expand your set anyway, ez-curl bars, dumbbell bars etc etc and having a set of oly plates will let you do anything you want.

I have 4x 20kg plates, 6x 10kgs, 4x 5kgs. and that pretty much lets me do any variety I want.

How much weight do you plan on using? The Power Block adjustable dumbbells offer a range from 3 pounds to 90 pounds per hand. (This is through two different sets with two "addons" for the heavier set. the heavier set stops at 50 with no additions). If you plan on doing an exercise with more than 180 pounds total you'd need the bar and several/many plates. The dumbbells are easy to store out of the way, don't take up much space at all and are versatile. Just my $0.02

I use both at times. It really depends on your goals and what your working towards.