I shoot the tightest groups with my SigSauer P239, which was never designed as a target pistol (it's a compact slimline for concealed carry). The Sig P228, which is my most recent addition to the collection, is probably my second-most accurate pistol. I still love my Glock 19, but I find that my groups are slightly larger.
I've competed in 3-Gun and IDPA with the 19, and I've done fairly well with it. I'm hoping to sneak out of work one Saturday and bring the P228 out and see how I do. I would go with a Glock or a Sig before I'd bring a Beretta out to a match, since I know that I would forget to wipe the safety off before my first shot.
At our IDPA matches, you'll see equal numbers of Glocks, Berettas, and Kimbers on the firing line. There's a scattering of SigSauers and HK USPs, and a couple of K and L-framed Smiths.
Choose the pistol that fits you the best. Accuracy will follow.