Searchbar and/or Google it on you're own, in 5 minutes you will have all the info you need to make an educated decision.
That being said, both of the skis are the exact same, the only differences being that the alpha's are stiffer and have a racebase, and the halo being softer (mid flex compared to other skis) and a more durable base.
I would get 170 Halo, since you are not very heavy the alpha would probably be to stiff for you, unless that is what you want.
Also a point to note is that both skis have armada's elf shoe technology (taper in the tips/tails with a rocker/camber/rocker shape) and they ski weird the first day or so, and are not close to being traditional skis, so you may want to consider the ar7's or the el rays. There is a thread called "rockered park skis" that should do a good job on explaining what rocker in a park ski is, its advantages and disadvantages, and a few recommendations.
Sorry if this is a little un organised but im on mobile, I hope this helps you!
Ski the Brim