Ron over at FTW has got a collaborative post going on about your must have unit. For me my must have unit choice has very little to do with actual gaming effectiveness or points cost. I've pretty much always collected Guard, and from the very first time I opened up the codex, I've thought stormtroopers were sweet. I remember seeing them in the codex and thinking, wow, a save that's better than 5!
I used to field a squad of five against my friends chaos army, and they would always end up getting squished in close combat or slammed by bolter fire. I never was any good at winning games when I was younger...but they made it on to the table almost every time. I always liked the idea that they were the best of the best, even if I could never get them to play that way.
Since then I've pretty much always fielded them, and in 5th edition they make a sweet punchy unit when you put them in a chimera and outflank to the rear of a tau gunline. The new hotshot lasguns are sweet, so now more than ever the stormies have a place in my army not just for the fact that I've always used them.
Stormtroopers are my must have unit, because, well they're models that have always been in my army, and it would be kind of weird to play guard without them on the table.
As a side note - I was just reading through this thread on DakkaDakka, and I noticed that the ratling in the background of this picture looks almost too much like the new mini (you know the one, sniping around the post, with the apples) not to be some kind of homage. I thought it was interesting to see the sculptors drawing on stuff from 2nd ed for new sculpts!
