I remember when i joined 2 1/2 yrs ago, all we had were the Starters. And I can still remember buying the Tour Starter driver when it was offered ... only 5 yrds longer, but it was a HUGE 5 yards. That was about the time that Bethpage was released, and BP from the black tees with Starters was beyond tough. The extra 5 yrds or so with the Tour Starter was very often the difference between fairway and rough on several holes.
If you want 1 club that will make a difference NOW, go for the best driver that your level & credits allow.
Edit- Ninja'd by Josh..........but he's exactly right .... the best wedges in the world will do you absolutely no good if you can't get in a position to use them! Same goes with a better putter... while you make more 25-30 footers with it, it would be much better to NOT have to try to make them.