Since you mentioned that you are buying used, if you find a Gitzo, be sure to check out one thing about the twist locks. As Alvin pointed out, the ability to unlock multiple leg sections with one twist is very valuable. The old Gitzo's required that you unlock/lock each leg segment independently. This is way slower than the lever locks used in Manfrotto (Bogen). The problem though with lever locks is that always loosen over time (almost always at the wrong time) and you need a wrench to tighten it. And, again as someone above noted, the lever locks always seem to snag something.
The more recent Gitzos have some sort of clutch mechanism that allows you to grab 2 or 3 locks at the same time and twist allowing you open/lock much more quickly. So if you look for a used Gitzo, I recommend that you get one with the ability to twist more than one knob together.
And as you might imagine, I much prefer twist locks over levers. As for the head - agree that you need to buy a good one so as not to have to buy another when you discover that the weight rating is less in the real world than it says in the promotional ads. Remember that a head that will support your current rig may not be useable if you buy something larger like an 80-400, etc.
And lastly - I strongly recommend that you do not buy a Manfrotto head, not because they are bad heads, but because it uses a proprietary QR system rather than the ubiquitous Arca Swiss style clamp.
The more recent Gitzos have some sort of clutch mechanism that allows you to grab 2 or 3 locks at the same time and twist allowing you open/lock much more quickly. So if you look for a used Gitzo, I recommend that you get one with the ability to twist more than one knob together.
And as you might imagine, I much prefer twist locks over levers. As for the head - agree that you need to buy a good one so as not to have to buy another when you discover that the weight rating is less in the real world than it says in the promotional ads. Remember that a head that will support your current rig may not be useable if you buy something larger like an 80-400, etc.
And lastly - I strongly recommend that you do not buy a Manfrotto head, not because they are bad heads, but because it uses a proprietary QR system rather than the ubiquitous Arca Swiss style clamp.