There are indeed many aficionados of Guinness that could probably spot the nuances between pints served in different pubs. What I can say, even taking account of my somewhat more untrained palate, is that the difference between a pint served in North America - indeed, in most other places in the world outside the island of Ireland - and Dublin is marked.

The taste is different, the temperature is different (which is a factor in the taste, of course) and the serving method is different. That's what you're going to notice, not some tiny variance between pubs.

Rather than worry about finding the absolute best, which will vary depending on an individual's taste buds, discover and embrace the atmosphere, architecture and craic in as many different pubs as possible. You'll have a far more fulfilling experience as a result. There's an awful lot more authenticity to Dublin than Temple Bar.