The standard view engine has the most functionality in terms of both Visual Studio compatibility and ASP.NET MVC compatibility, but it's the least readable.
Spark view engine is usually preferred by most people, mainly because it has a nicer view, and it's mostly "compatible" with the designer crews, who only know how to create HTML pages. It also has some C# IntelliSense support for Visual Studio 2008. If you need to give out the view to designers Spark is the best choice.
Coming from the rails/merb world I actually prefer NHaml, because it's very expressive, and DRY, although it's not really "designer friendly". It also has some C# IntelliSense support too. (N)Haml is a view engine that people either hate or love because it's terse nature.
As far as i know these are the only three view engines that have support for C# Intellisense (and only for VS 2008, although work to get them run under VS 2010 is in progress), which can help a lot, and which usually people who want to switch from the "standard" view engine consider a "must-have".
Don't forget however that you can mix view engines in a project, so you can use the standard view engine where you need it's functionality but switch to spark/nhaml/anything else if they suit your needs better.