In recent years I've used Schwalbe presta standard and light, as well as Conti, Bontrager, and one or two No-Names, depending on what was available when I needed a new tube. The Schwalbes have been the best, all else equal -- especially, free of leaks around the valve collar and free of apparent manufacturing defects such as leaks along the seam.
Interestingly, I've never had problems with valve cores working loose, but after reading posts on the Forum, I've bought a Park valve tool.