I used extensively for work and would always recommend them when using stranded wire. I also used them for a new controls board for our programmers to be able to develop and train with. It doesn't really change a much for the power distribution board but it makes it much easier for the pneumatics module and voltage regulator module.
For the size part of the question I used a range of sizes for the range for the sizes of wire on the robot. With the different colors it kind of gives it a color code for the different sizes of wire.
McMaster has the full range of sizes with choice of colors. You can probably find them cheaper else where.
http://www.mcmaster.com/#ferrule-terminals/=1063bi3