Good question...
It will help your career progression to get on with it faster, and an additional type rating will help increase your app score as well.
The CRJ is a bit simpler to learn than the 175 is some respects (no RNP). Talk to people and see what they say about the training program at your company.
For me it would come down to how good of a student I am... if you did fine in your previous 121 (and 135) training events, relative to your peers, then I'd be inclined to take the first upgrade regardless. If you struggled relative to your peers then maybe wait for the 175.
I once bypassed upgrade on a new plane to wait for my current plane six months later. Just being lazy. Then the music stopped. Five years later I upgraded... on the new plane, which I could have been flying as a CA (albeit very junior) for the previous five years.