If you're 4wd, you will need to change both front and rear gears, that gets pricey. But as far at 4.10 or 4.56, it really depends in your preference. If you are looking for fuel economy, either gear ratio will help your overall city mileage, and hinder your freeway mileage. If you do more city than anything, you will see an overall gain, better gain with 4.56s. If you do mostly freeway, you will lode mpg. More so with the 4.56.
Now if none of that matters, then 4.56 will give you the highest gain in torque, and the biggest change in driving characteristics. You might even be able to peel out with 4.56s on that lethargic v6.
Its costly though, parts and labor for 1 diff can run you 500-1000. Add a front diff into that and its 1000-1700 smackroos gone in a blink.