Here is the London Beer Guide's list of the Top 10 pubs in London.
1. Craft Beer Co. (Clerkenwell): few other bars in town can compete with this CBC outpost when it comes to beer selection. With some 37 taps split between keg and cask, and c. 100 bottled beers, you can always find something. The casks are essentially always from UK breweries, while the kegs tend to pour beers from the USA, Belgium, Scandinavia and some of the more progressive UK brewers. The pub can get pretty packed during peak hours but thankfully there's a bit of seating upstairs in addition to the bar area downstairs.
2. Euston Tap (Euston): In terms of raw beer range the Euston Tap is one of London's best bars. What the place may lack in cosiness it more than makes up for with 19 keg lines and eight cask lines. As one of London's first craft beer pubs (their November 2010 opening makes them ancient on the scene) these guys have built a name for themselves by consistently bringing in great beer from around the world, as evidenced by the beer menus overhead and the glowing beer fridges below them. You can almost always find stuff from Arbor, The Kernel, Redemption, Thornbridge and others on tap. The bottle range features a host of gems, with an extensive Belgian range, in addition to good selections from the US and Scandinavia.
3. The Cock Tavern (Hackney): I love this place. If I were ever to own a bar, I would want it to look like the Cock Tavern. The place is spartan in its aesthetics but fairly indulgent when it comes to the beer, especially local beer. The Cock Tavern acts as brewpub for Howling Hops; as such, you will always find c. four Howling Hops beers on cask and a couple on keg. This pub also does an excellent job supporting London breweries and you will routinely find the likes of Brew By Numbers, Brodie's, The Kernel, Partizan, Pressure Drop, Redemption and Weird Beard on tap or in bottles. The pickled eggs ain't bad, either.
4. Cask Pub & Kitchen (Pimlico): As one of the first beer-centric pubs in London, this place was well ahead of the pack when it opened back in 2009. While the competition has ramped up significantly in the ensuing four or so years, CPK still stands out. The tap range (on both cask and keg) is stellar, but CPK really shines on the bottle front, with in excess of 100 beers lining the fridges. They also do a nice food here.
5. BrewDog (Shepherd's Bush): With the latest of their London bars, BrewDog ushers in the era of the Craft Beer Superbar. With some 40 keg taps and several dozen bottled beers this place has one of the best selections in London. The ambiance in here is a bit more laid back than the other BrewDog bars in town (Camden and Shoreditch). What's more, there's an abundance of space that helps to keep things mellow. As with all BrewDog bars, the staff is well trained and efficient.
6. Craft Beer Co. (Islington): Following a model similar to CBC Clerkenwell, the Islington branch offer much the same in the way of beer offerings and service, just in a different environment. There tends to be some overlap in the beers offered across CBC locations, so expect plenty of options from the UK on cask and keg, plus beers from the US, Denmark, Belgium (among others) on keg, and everything imaginable in bottles.
7. Earl of Essex (Islington): The Earl of Essex has a great setup. First and foremost, the beer selection is strong, and this pub gets some offerings you won't see at other pubs in town. Both cask and keg offerings tend to focus on UK breweries, though you will often find something German and US beers on keg. Bottles generally feature non-UK breweries. Aesthetically, this place is really attractive. The circular layout of the bar gives the Earl of Essex a fairly unique feel compared to other London drinkeries. Then there's the back garden, the stylized tap handles, the clear and informative beer board...I could go on.
8. Craft Beer Co. (Clapham): It might seem redundant to have all these CBC pubs on the list, but in all fairness, they're just way better than most other beer-focused pubs. The Clapham branch is the most recent opening in the CBC fleet and it offers the same dynamic range of cask, keg and bottle. I happen to love the ambiance of this one, perhaps more than the other three in town, as it feels a somewhat homey inside - not too dissimilar to Islington but quite different from Clerkenwell or Brixton. They also have an abundance of outside seating, which I'm sure will go over well in the warmer months.
9. The Harp (Soho): Here's a place that has been around for a while. The Harp is great in that it is, first and foremost, a traditional pub. But that doesn't mean they haven't embraced the beer renaissance happening around them in London; you can almost always find Kernel on keg in here. On cask, Dark Star is a permanent fixture. There's also an impressive range of ciders in case you're into that kind of thing. The pub itself is beautiful and, if you can find a place to sit, the upstairs room is a great place to hang out.
10. The Southampton Arms (Gospel Oak): With its no-nonsense approach to life, the Southampton Arms is a nice throwback, and their slogan really says it all: "ALE CIDER MEAT". They only take cash, they don't take reservations, and they are dedicated to selling beer and cider from small, independent UK producers. No complaints here, since all the best beer coming out of the UK right now is from small, independent breweries. The only downside to the Southampton Arms is that it isn't the biggest pub in town. As such, you'll be lucky to find even room to stand during busy periods.