Hi Hipeboy!
I have a SD PS 170, and had a PS-2A. Here are my .02:
1. Depending on your situation the PS-2A might not be loud enough. I found it to struggle in a situation playing with another guitarist using a tube amp.
2. Unless you want all the additional features - which are very cool, the PS-2A may not be worth the extra $$$.
I did some comparison audio and video captures, and honestly, the difference between the PS-170 and the PS-2A were small enough in a mix that I could not justify the additional expense of the 2A. (I have other methods for reactive load boxes already, and do not need the FX loop functionality.)
For me, the extra weight, and cost, did not pencil out.
Again, for me, the LX-II is a better option - it does cost more than the PS-2A, but fits in one RU, is stereo or mono (100 watts) and it just does something for me - I can't really explain it. I did the same comparison mixes and the LX-II sounds a little better in the mix than the PS-170, but when isolated, there is no comparison at all.
Sometimes, I still gig with the PS-170 - as you mentioned its compact, and light, and is powerful enough to hang in a band context. I did like the PS-2A, but it just did not work for my needs. I like the LX-II so much that I bought two.
Best of luck on your search!