Well, I've never found Jack Daniels in a can, so I will have to say bottle.  

The internet is a wonderful thing:

http://www.ivo.se/guinness/serve.html

8-)

Get it straight from the tap in Dublin and see how cold it is.

The internet is a wonderful thing:

http://www.ivo.se/guinness/serve.html

8-)

Get it straight from the tap in Dublin and see how cold it is.

They do that for the tourists who do not like their beer served warmer.  These pubs will typically have two Guiness taps.  One cold and one warmer.  

From Guinness' own website

GUINNESS® Draught is best served at 6°C (that's 42.8°F), with the legendary two-part pour. First, tilt the glass to 45 degrees and carefully pour until three quarters full. Then place the glass on the bar counter and leave to settle. Once the surge has settled, fill the glass to the brim. It takes about 119.5 seconds to pour the perfect pint. But don't fret. It's worth the wait.

Can all the way...

1.  Cools quicker.

2.  Better taste.

3.  Cheaper!!!

Nothing beats a glass bottle.

-Ike

Glass bottle of what?    :

A GLASS bottle, coke seams to taste better in a glass bottle!  ;D