Consider reliability, weight, output (both hp & lb-ft), fuel efficiency, smoothness/drivability, etc.

Some might throw in 'tunability', but I'm more curious about your opinions on the stock package.

Bonus question: If the 2.7T isn't a 10 to you, what engine package (from any manufacturer) is?

Having owned one for 2 yrs, I'd rate the 2.7 as at a 7. Here's my list of 'naughty' and 'nice':
+ torque! (full range)
+ upper end hp
+ aural gratification (turbo spool-up, valve-train sound at higher rpms)

- weight of engine package
- fuel efficiency (admittedly the A6 is heavy & quattro doesn't help the numbers)
- overall complexity (30 valve head, twin turbos w/i-coolers)
- propensity to develop minor oil leaks

Much as I dislike the Chrysler/Dodge group, their current 3.5 liter V6 puts out 250 ft-lbs/250hp. And Honda/Acura gets 240+ from their totally bullet-proof V6's. And the BMW line of 6's is legendary for their power characteristics & longevity.

In my motor "hall of fame", I've actually got the Honda 1.5 liter line of inline 4's. 200,000 miles on these motors are nothing. Just gas & oil, they're happy to run forever!

My Audi warranty expires in May. I think I'll have to chip it in order to love what's under the hood as much as I do the rest of the car (2000 A6 6spd).