While 1.5x or 2x GVW is a easy starting point, I feel it is more intuitive to look at the actual load resistances likely to be encountered. If miring your rig up to the fenders isn't remotely probably, then why plan for it? I'm all for 'overkill engineering' and 'better safe than sorry' but we don't all need an Warn 16.5ti on our rigs when a 8k or 9k or 10k, etc would do the job.
I listed these for a 5000lb rig but you can do the math for your setup given the types of winch recoveries you would be likely to encounter. My final recommendation was to run the biggest winch you can cleanly mount and your suspension will support.
Lets assume your in your 5000lb (loaded) vehicle.
Surface Resistance:
1/10 LW (500lbs) to push a free wheeling rig on a hard, level surface
1/3 LW (1700lbs) to push a free wheeling rig on soft surface, grass or gravel
(add a broken rig to either of these situation and they can easily multiply the resistance and therefor the needed winch).
Damage resistance:
2/3 LW (3400lbs) to move a vehicle if the wheels cannot rotate (bound up axles, brakes, etc.)
Lets look at more common winch needs:
Stuck in mud:
Wheel Depth Mire (up to wheel hubs) = Resistance is the LW (5000 lbs)
Fender Depth Mire (top of wheels) = Resistance is 2x LW (10000 lbs)
Cab Depth Mire (over the fenders) = Resistance is 3x LW (15000 lbs)
And the above figures can increase (or decrease) based on the slope your working with:
Working with slopes:
Uphill Winch Pull (pulling up slope)
15 degrees - add 25% LW (add 1250 lbs)
30 degrees - add 50% LW (add 2500 lbs)
45 degrees - add 75% LW (add 3750 lbs)
Downhill Winch Pull (pulling down slope)
15 degrees - subtract 25% LW (minus 1250 lbs)
30 degrees - subtract 50% LW (minus 2500 lbs)
45 degrees - subtract 75% LW (minus 3750 lbs)
So lets say your 5000lb (LW) vehicle is stuck up to the top of its wheels and getting deeper as you continue to try and work it free. The nearest winch anchor is just over a 30* angle a above you. Your calculated load could easily exceed 12,500lbs. Far more than a 5k winch can even do single snatch blocked. Now remember that a winch is only capable of their rated capacity on their first layer of wrap, that which each additional layer they lose capacity. So unless you want to be re-rigging constantly to keep your winch in its optimal range (this goes for needing a snatchblock too), it makes sense to select a winch that will be capable of handling these loads. Sure you could use a complicated system of multiple snatchblocks. But the added cost of blocks and extension straps in conjunction with the limited range you would end up with (a 125' cable is good for lets figure 100' on a single line pull, yet only 50' with a snatch, start adding additional blocks and you'll end up with just a vehicles length of range each rigging). There will always be compromises, due to size, weight and mounting you can't fit the biggest winch on every rig, but I would do my best to fit the biggest I can.