Broken Steel fixes a plot hole at the end (I won't spoil it)

Broken Steel & Point look out for sure. broken steel raises your level cap and point lookout is just awesome in general. a whole nother big map

Broken Steel and Point Lookout are better IMO. But the GOTY has them all, is much cheaper than buying them separately(It's the same price as the normal game on Steam for whatever reason...) so get that if you can...

Why not get the GOTY Edition? You get all of them much cheaper than if you buy them separately. Unless you are low on money, in which case get Broken Steel and Point Lookout. That way you can continue after the main game is finished.