A lot of people prefer buying kits sized so each vial lasts around a month. So if running a moderate weekly amount of the third compound, a mid-size kit tends to be the popular pick. For those okay with more risk who want a mixed vial to sit in the fridge longer, a pretty common approach, going bigger on the kit size works too, though that means stretching the same vial across roughly ten weeks. Really comes down to your own comfort level. Generally the bigger kits work out cheaper per milligram. If you're only running a very small amount, a huge vial probably isn't worth it. And if you're just starting out and unsure where you'll land, assume you'll be increasing gradually over the coming weeks.