All beer is either an ale or a lager (or hybrid). This is not determined by color, taste or alcoholic strength, but by the fermentation technique and yeast used in brewing. The only detectable difference between an ale or a lager is the presence of esters in ale. These esters are produced in greater quantities during hot fermentation.
Lagers are made with lower-fermented yeast strains that are kept at cooler temperatures (around 40-52°F), while ales are made with a top-fermented yeast that operates at warmer temperatures (around 55-77°F, generally). Although the differences between ale and lager beer are many, having a better idea of the facets of the brewing process and the ingredients that affect the final product allows you to better appreciate the differences between the two varieties. Pilsners beers, attached lagers (think big brewery beers made with lots of rice and corn), schwarzbiers, bock, doppelbock and lager Vienna are prime examples. The main difference between ale and lager beer is reduced to the type of yeast, fermentation temperature, color and taste.
Ales are fermented with top-fermented yeast at warm temperatures (60° to 70° F), and lagers ferment with lower-fermented yeast at cold temperatures (35° to 50° F). Lagers also go through an extra step that beers don't go through, one of cold conditioning to develop greater clarity. This stage allowed more yeast, protein and hops to settle out of the beer, dramatically improving clarity and reducing cold haze. Ale allows itself to be extremely experimental with real beer festivals that feature some of the best concoctions people have ever made.
Although lagers have enjoyed significant market share, the strong growth trend of ales in microbreweries and imported beers offer an excellent alternative for those who prefer a beer with a little more substance. Choosing what is best between lager and ale is like comparing a burger and a cheeseburger. Both have their own unique flavors and characteristics that make them enjoyable in their own way. It all comes down to personal preference when it comes to deciding which one is better.
One of my favorite things about beer is that pubs will change depending on the beer they have in stock so that you can really find that special drink.