Tripods are intended to give you a stable platform for you camera with lens or scope/binoculars.
Are you a photographer or a bird watcher, because you may need different products. An all round favourite are the Benbo tripods. They are very well designed and with the right head will provide the performance you need.
If you are a photographer do you need a tripod designed to cope with water and mud? Are you going to be carrying the tripod around on hikes?
Stability verses weight are the criteria. The heavier the tripod the likely hood is that it will stand abuse and give you supreme solidity. Again Benbo fits the bill but I prefer Manfrotto as a tripod as the multi position lever design of the Benbo becomes very awkward if you are trying to move back to photograph a large group at a wedding unless the ground is level. However if you are out in the wilds and need to get down and dirty hey the Benbo grabs my ********! Another brand worth checking out are Gitzo generally known a s a profesionals brand, but do not seem to have the same following here in the UK as the other two mentioned before.
If you are intending to carry your tripod some distance check out the weights. A cheaper product, Jessops,Slik, Vivitar etc may be all you need, also consider a MONO POD, MONOPOD, fantastic bits of kit for a quick aditional support, again I have a Manfrotto product and would not be without it.
Always consider whether a tripod is necessary at all, you can always use Fence Post, gate or Street Lamp, Walls or Vehicles to lean aginst for stability. A cushion or bean bag on an elevated surface suck as a rock, car bonnet/roof or even use someone else to rest on their shoulder!
How high do I need to go? Do you need anything above head height? also how low do I go 10cm? 100cm? Some tripods allow the centre column to be reversed so that you can go down as well as up. How quick/easy do I need the tripod to be? Am I working under pressure trying to catch a moving object? The more adjustments you need to make, leg extensions, pan , tilt and up/down view on the head etc.
How solid does the tripod need to be? - this depends on the weight of the equipment you use Camera+lens etc (also how long is your lens?)
The Benbo tripod or simular has a single bolt controling the direction/spread of the legs (but can be fiddly) and then you still need to extend the legs and then adjust the head,
A Manfrotto (or similar) by extending the legs you can adjust to suit uneven ground, if you set the tripod level the only head adjustment is the pan and up/down.
Which is quickest and which is best is personal choice.
Probably the best question to ask yourself is how often do I really need to use a tripod?
THE TRIPOD HEAD
Ball and socket (Ball & Socket) or better still the Manfrotto grip heads are the quickest, but for solidity, accuracy and smoothness you cannot beat the standard pan and tilt head especially if you are using video. Again check size, bulk and convenience (also can they take the weight of your equipment).
For nature photography the Benbo (Kennet Engineering) is the recognised leader of the pack, but anything else depends on your need and choice. Why is it most proffesionals seem to use Manfrotto as their general use tripod?
If you ask yourself all of these questions you will have narrowed down the choice, the question is how much are you prepared to spend but as most photographers own a tripod which never sees the light of day are you wasting your money? Because these tripods are out here they pop up with little use on ebay for bargain prices, but always do your homework as to what its value new would be (or was) as you should not need to pay more than 60% of the original value.