Sierra Matchkings use a secant nose (ogive) while the Berger VLD's (and most Hornady Amax) use a longer tangent ogive. That means the SMK's are more tolerant of a jump to the lands while giving superb accuracy, and thus can be loaded to magazine length and shoot very well.

I think very highly of Berger bullets, but the long tangent ogive means that you have to fiddle with the seating depth a lot more to achieve very high accuracy. Personally, I do not like loading so that the bullet is in the lands. That's my opinion on why I think SMK's are so popular. That said, I like both VLD's and Amax bullets too.