I choose the P226 for all the same reasons I’d choose the M17 over the M9. No locking block to crack at inconvenient times. That also means fewer parts and simpler takedown. Other than that, they are quite similar. I find it interesting that there wasn’t the same amount of ire towards them M9 (as toward the M17) when it won the contract due to a lower cost.
Also, the open slide of the Beretta has never bothered me. I can understand why it would bother some people, but i’ve put quite a few rounds through it, and I’ve never seen an issue due to grime in the slide, as it’s a pretty tight seal around the barrel. However, this point is obviously moot when compared to the P226 and M17. I just thought it would be worth pointing out its a non-issue. What is more of an issue is micro fractures developing in the slide, as it is not as structurally sound. If you disassemble a Berretta and hold the slide by one end, you should be able to hit it with the recoil guide rod and have it sing like a tuning fork. If not, it means that you have fractures within the slide blocking the reverberations. Not a catastrophic failure, but another non-issue with the P226 and M17.