Trad Climbing →
What's the best spring-loaded camming device?
This is a contentious topic and your preferences may be unique to the style of climbing that you're doing. That said, for a general purpose, the most popular medium size cams are Black Diamond Ultralight C4s, followed by Metolius Ultralight Master Cams, with Totems coming in third.
For thin crack climbing or aid climbing, the Black Diamond X4s, CCH Aliens, and Totem Basics are popular, with Metolius TCUs and the regular Totems being particularly useful for narrow or flaring pin scares respectively.
If you're just starting out with traditional climbing, it's a safe bet to purchase Metolius or Black Diamond cams as these are well tested within the community. Further, the colors of these cams serve as a lingua franca to describe the size of various cracks. When you share gear with someone, it's very helpful to know at a glance what size piece will fit a given size crack.
For sandstone climbing (especially Navajo Sandstone), consider using Metolius Fat Cams or Metolius Supercams for more reliable protection.