Replying to Best Ski Size?

Obviously there is no best ski size because it depends on the skier's dimensions, the mountain conditions, and what you're doing. I have two pairs of skis, some old 2008 or 2009 (maybe even 2007) Dynastar Troublemakers 155, and some new warranty replacement Dynastar Sixth Sense Spins 167. I usually use my Troublemakers even though they're supposedly too small for me (the tips are up to about my chin). The Spins are apparently perfect for me in terms of size. I feel a lot more comfortable on the Troublemakers in the park, but the Spins are definitely better for all mountain skiing. For example, I can spin up to 5 on my Troublemakers and love doing BIG 3s, but when I was in the park on my Spins, my rotations got fucked up and I can't spin as fast and actually somehow landed on my back a few times. I feel like my body is spinning but my skis aren't keeping up and actually throwing me off because of the length and mass. Most people I know don't ski on such short skis, except my brother (he got me into the habit). I'm wondering if this is normal, or if I should practice with longer skis in the park to break out of a potentially bad habit? Thanks guys.