I don't think it matters which gun you choose and I don't think you will perform better wtih one gun over the other.....long term. It is likely you'll perform better on drills heavy on gun handling with the gun you're most familiar. It's likely you'll perform better on slow fire accuracy drills with the trigger you are least familiar.
Here's a little story that you might find interesting:
A few years ago I started practical shooting and just happened to have an M&P 45 so that's what I used. I loaded it to minor and shot production. My good friend Mr. White told me how I could win a bunch of Glocks in GSSF - besides having a bunch of fun. I didn't really care about Glocks (just preference) but a "free" gun is cool so I borrowed his G21 and won a few. I liked the idea of winning free Glocks so much I thought it best to shoot them full time so I took my certifciates and set up a G34 for USPSA Production. At the same time I was a Ben Stoeger, Steve Anderson, et al. nuthugger and had converted my garage into a Dry Fire dojo. But there was a twist.....I had already loaded up about 10,000 rounds of ".45 minor" for my M&P and with winter (don't shoot in the rain) upon us there was no way I would shoot it by the following season to make a clean switch. And there was no way I would let it go to waste. So I decided I would shoot my normal dry fire and live fire training regime throughout the year and whenver I ran out...I would switch to Glock. Just so happens I ran out about 2 weeks before the "State Match." I won the local match the week prior and went on to finish top 10 overall and 3rd A. A few matches later I made Master.
Moral of the story... I was training and improving it was an uphill progression... maybe the climb was slightly stutterred at the switch but it was all uphill.
I like HK's, M&P's and even XDM's over the Glock and if it wasn't for GSSF I wouldn't be shooting them. But all of the guns I mentioned are so similiar I doubt there is any noticeable difference in what I can do with one over the other.