I think stock/chassis selection is a very personal thing, no one can tell you what's best for you besides you, it's a "different strokes for different folks" thing (a great example is what
@jthor mentioned, the new 2024 PRS champ Ben Gossett is still running an MPA BA Comp chassis, which hit the market in 2015). But, buying new today, the Vanquish is probably the safer bet over a Matrix Pro as it's the newer design.
Personally, I seem to dislike aluminum chassis' (or at least haven't found one I like), and after having tried more than a few, I always end up back with my Manners TCS that I've had for ~4 years now.
I'm probably one of the few who dislikes the MDT ACC Elite, as they're surprisingly rear-heavy. To get it to balance right for me, even while running a fairly stout 26" Proof Comp contour, I had to use all 5 internal weights and 2 sets of mlok weights as forward as possible on the rail to get it to
almost balance how I like (and still wanted more weight up front to really get it where I wanted). But, at that point, I had a ~25+lb rifle when loaded (which is already heavier than I like). Then, there's the recoil impulse feel, the aluminum chassis' are the opposite of dead and don't soak up much, to me they feel like they transmit the recoil impulse to one's shoulder more directly than some other chassis' (for comparison, my TCS balances better and has a deader recoil impulse at ~22lbs loaded).
I think for bang for the buck the Vanquish production rifle is pretty sick and worth a try. Its Vanquish chassis is MPA's new hotness and the new rear design looks promising as far as not having to load it down with weights out front to get it to balance right. Since it's new on the scene, if you don't like it and want to try something else, you'll have a good barreled action and trigger and the chassis will be easy to flip as it won't last long in the PX.
