^^^
So, I got alot of time to kill while my family is over for easter dinner because they're all older or younger then me by 15 years. So, here's my argument on why you should pick skateing over blading if you have to chose one.
I am going from experience as I've done both for atleast two summers (I do them when my bikes down for repairs). I highly suggest trying out both to understand for yourself. Now rollerblading will help your airs out more then skating, but helping your rails and overall spacial awarness and balance go to skate boarding.
Right off the bat I have found most grinds on blades get you lower to the rail which gives you a lower center of gravity. So once your feet land near the right place it's easy to lock on and slide the rail until you want to come off. Also with the grind plates on the blades like the h blocks, I find you dont have to be super precise you just have to catch part of the grind plates and they more or less lock you on, where on a skate even if you 50/50 you still can slide around on the rail. One more thing with rails is most slides on blades both feet are over the rail while on a skate this rarely happends and sometimes not even one foot is over the rail, forcing you to alter your body postion alot more to stay balanced.
But rails aside a skate board is much less stable then a pair of rollerblades (I bet no one could knock me off a pair of blades but it would be easy to just push me off a board, try it with a friend if you don't beleive), there for if you can master your balance on a skate you'll have a higher degree of balance then on a pair of blades.
As for spacial awarness it's quite simple your board not being attatched to your feet gives you another whole object to have to be spacially aware off. Say your going to ollie over something, on blades, you have to be aware of your wheels clearing the object then where your blades are going to touch down so you can balance for the landing; on a skate you have to be aware of getting your wheels over the object but then on the landing you have to be aware of not only where your wheels are going to touch down but the position your feet will touch down on the board so you can balance for your landing. And that's just simple stuff imagine the spacial awarness you'd need do bust out a flip trick with a 180 over the object. Plus the fact that skating is so precise, like your foot a 1/2 in the wrong spot will make you crash or mess up a flip trick.
So that's my argument with out getting into all the biomechanics on why skateing would be better for skiing then blading, I'm not getting into which one is more fun because thats up to the person. And I do a shit load of sports and activities (ski, hockey, football, I did cometitive tramp and now coach, DH mountain bike, BMX, skate, rollerblade, soccer, surf, snowmobile) and out of all of them I find skateboarding to be the most technically difficult and it's this was the fact that attracted me to skating a bit in the first place.
So in conclusion if you want to progress your skiing more I would say skate boarding would be better and also for the dude that made the thread where cost sounds like an issue it's a bit cheaper for the equipment. But you should do both if you can...well actually the more sports you try the better your balance and spacial awareness so do as much as you can because every sport will bring something unique that will improve your overall abilities.