Is it better to wait til you are/almost are out of gas to get more or to refill the tank whenever you can regardless of how much is left?

They are all putting to much thought into it.
Being a mechanic i hear all of this all of the time.
1. If you have a full tank, its not gonna rob your gas mileage enough to matter.
2. Condensation will not hurt anything. It's not nearly enough water. You would have to let your vehicle sit for an extended period of time.
3. You guys, he/she knows there time i'm sure. they just want to know whats better for the vehicle.

-But, Looney Ape was right about not running out of gas. If your vehicle is carb then its not TERRIBLE but not good either, if you have fuel injected or throttle body definitely avoid running it dry.

So all in all, it doesn't matter, just don't run it dry.

I have read the answers posted before mine and they are all very good. A lot of the answer depends on the weather, how far to a gas station, the time of day etc. I used to live in ND in a small town miles and miles from a good hospital and any gas station that was open after 6 pm. I always kept a 1/2 tank or better since I never knew when I would be called and need to drive at any time day or night or in any weather. Also, in the winter with rear wheel drive, keeping a full tank was better for traction.
Many good answers, it is true that gas weighs about 7 pounds per gallon so keeping 10 or more gallons less would save a little on the weight you have to pull. And, if you don't have to drive extra to find an open station, adding often would be OK. With the prices now, I always fill completely up and run almost empty since I live in an urban area now and don't want to spend any extra to drive to a station. I also now fill when I'm near a cheap station because they are miles from when I live.
Good question!!

1/4 and I refill soon

Not where it snows....

Driving with a full tank makes the vehicle heavier and therefore it uses more fuel. If one wants to drive economically, it is recomended to drive until the tank is nearly empty without taking the risk of running dry.

Just make sure you do NOT run out of fuel because there is stuff in the bottom of your tank that might cause problems if it's sucked into the fuel injection system.

You should never have less than a half of tank of gas in the car especially in the summer. The morning condensation adds water to the tank. I usually have at least a half a tank.

umm not really.. what if you do run out of gas on your way to the gas station? i fill it up when its not quite there but to the point where its almost to the red

Such depends upon your willingness to go for long hikes carrying an empty/full gas can, all the while remembering the plot line for some "out in the sticks, movie concerning cannibals".