Again, it depends on your style, preference, and strength. I'm not much of a spinner - I've got relatively strong legs, and spinning tires me out more than using strength to "mash". This is partly due to my bike choice, a cross bike, which doesn't have the gearing for spinning. That bike is mechanically unable to "spin". While many here spin up hills, I'll alternate between standing and sitting climbs (depending on the how long the hill is). And although "mashing" bothers a lot of peoples knees, it doesn't bother me and I grew up with knee problems. Do what feels good to you. If you have the gearing, and you find that riding like you do tires you, give spinning a try. If you're fine doing what you're doing, keep doing itEveryone is different.