I've done both - measurements and template. You can get away with measurements only but you may need to do a bit of chopping and resetting measurements the first few times. Once you've got it right though the results can be very good indeed.

I also think the standard 6 measurements are not enough. I use 9 altogether:

#1. Circumference: 23 inches
#2. Front hairline to Nape: 13.5 inches
#3. Ear to Ear Across Forehead: 12.5 inches
#4. Ear to Ear Over Top: 12 inches
#5. Temple to Temple Around Back: 13.5 inches
#6. Nape: 5.5 inches
#7. From temple to temple over head: 9.5 inches
#8. From front of left ear round back of head to front of right ear: 11.5 inches
#9. Sideburns:
- Length - From bottom of right sideburn across top of head to bottom of left sideburn 14 inches
- Width – 3/4 inch