I'm sure this has been asked before but I can't find it. So...

When ordering speakers for a new setup (50/50 HT/music) in stages (over several months), what order would you order in? This is my guess:
1. mains
2. sub
3. surrounds
4. center

However, when considering the cost of a sub is almost the same as the center and surrounds combined maybe:
1. mains
2. surrounds and center
3. sub

Any comments on what provides the most improvement for money spent?