Gitzo are basically generally considered top tripods on the market as a brand.
Below them you get Manfrotto
Velbon and Silk are next, partly because they have some really low grade options, but they've also some very respectable legs now.
To the side you've also got Benbo which are high grade but do odd things (all 3 legs loosen at the same time and its more versatile for position adjustments but fiddly to get used to - some hate it some love it and its good for getting low or working in rougher terrain).
That's for the legs only. Tripod head wise many favour the Arca Swiss system (Kirk also make an identical system that you can use as well or with the Arca Swiss) that has quick release plates specific to tripod collars/bodies. The idea being that unlike regular ones on manfrotto and the like which use rubber to hold in place, the Arca Swiss design uses a plate with a raised edge that connects to the camera so it cannot turn around the locking screw at all.
You can, of course, get an adaptor that lets you use the Arca Swiss system on manfrotto tripod heads.
Tripod heads is more complex, but in general if its Kirk/Arac Swiss or Manfrotto its good.