For e60,
Get ACS Type IV.
17", you'll need to checked first whether it can fit and clear the brake calliper
18" will be nice, not available for Type IV unless replica.
19" will be superb.
20" will be excellent.
20" 2-piece will be awesome but it will cost your arm and leg.
My next ... :
e60 530d with M bodykit / ACS bodykit and ACS 20" Type IV 2-piece rims.