Each calculator makes assumptions about loss to grain absorption and process waste (mash tun loss, trub, etc.) so comparing different calculators without specifying the same process parameters for each is looking for confusion. Since you (I assume) have the BeerSmith software, start with that. You need to make a custom equipment file which represents your process with regard to mash tun volume and composition (specific gravity, weight), your boil off rate, process losses, etc. Once you have that down, BeerSmith will use this profile, once you specify this new profile in a recipe, to give you an estimate of the amounts of water you need to start with or add during the process.
Brew it and take careful measurements and enter them in the 'sessions' tab of your recipe where there are 'measured' values. If you are off in your estimations of boil off, water volumes, and gravity, you will see it pretty quickly. BeerSmith will also recalculate your mash and brew house efficiency and you can use this information to update your equipment profile for next time. The more accurate the measurements and the more time you spend getting the right information into the program, the quicker it will start giving you accurate estimates of what you will need for volumes.