Absolutely all 3 HDs
You'll find yourself using the parts manual more you may think.

 

I have not bought the parts manual, too cheap and have found almost all I needed so far on the HD website pdf's. Definitely a fan of the repair manual.

 

The repair manual is great but the parts manual gives you a great breakdown of just how everything goes together that the repair manual doesn't.

 

I bought a cd manual on ebay last year for about $5 I just print out pages of the work I want to do. Maybe eventually I'll have a printed manual

 

The service manuals are worth their weight in gold.

 

Zanotti's = $45.00

 

I've got both the service and parts manuals and they already paid for themselves in saved labor cost.

 

Amazon has HD manuals for decent prices too.

 

FYI, if you buy a, usually illegal, CD based manual, be aware that the manual is not searchable. This is because the manual is scanned (copied) and converted to pdf. So, all the pages are graphics, not text.

 

There is a free 2006 touring manual on pdf at www.carlsalter.com. At least there used to be. I like the pdf for quick searches (yes you can search this pdf), but I also have the printed manual. Download the free one for the time being and buy the manual later.