I used to be a big Speer guy, and I still am... but for pistol bullets, simply because they make the Gold Dots, the runner-up would be Hornady with the XTP. Incidentally, this mimics my choice in carry ammos as well. I shoot a lot of cast bullets in handgun as well... I get them from different sources... Montana, LaserCast (Oregon Trail,) or, quite honestly, whoever I can get .41 bullets from. If I had to pick one, I suppose Oregon Trail.
After my experience with Speer bullets in the .30-30, I've gotten completely away from Speer for rifle bullets. If I had to pick one for jacketed bullets it would have to be Hornady, not only do they make excellent .223 and .308 bullets for LR work (although the Sierra MatchKing is my favorite... but you said to pick one....) but the deciding factor is Hornady is the only company making jacketed .348WCF bullets. Again, I shoot a lot of cast in my lever-actions... Montana is my go-to because they offer the excellent RCBS 200grn .349" bullet for the .348WCF, with Oregon Trail as my runner-up there.