Everything depends upon what you need to do. It doesn't sound like you have much ORM experience because you enumerated possibilities without opining on any of them. They are all "good" - including EF v.1. They differ in what they are best suited for (which, I hasten to add, is a combination of what you want to build AND the skills, experience and community of developers building it). Please give serious thought to your problem and your context *before* you get balled up in product comparisons. Your choice of client technology matters tremendously. Are you serious about writing in ASP.NET Forms, MVC, Silverlight, and WPF? Why? If I may be bold, it seems your business objectives are unclear to you. If a multitier solution (e.g., Silverlight) emerges *from your business analysis* as the best choice, then EF (v.1 or v.4) will seem especially attractive. The momentum and educational resources in Silverlight data-driven application space are more abundant around EF. Take a look at CSLA, the forthcoming RIA Services from Microsoft, and my company's DevForce (http://www.ideablade.com) to learn more about being productive with Silverlight business app development. P.s.: Remember that the production release of EF v.4 isn't expected until something like March of 2010. You can get going in v.1 now (it's much better than the wags tell you); your transition to v.4 won't be difficult (especially if you insulate yourself from direct application-to-persistence-machinery contact with something like a Repository pattern) ... and you'll be glad you didn't bleed on the knife's edge of beta technology. Ultimately, IMHO, Entity Framework will be the big dog among ORMs. There will simply be more people who know it, have experience with it, can be hired to it, etc. I think other ORMs are easier and more capable ... today ... but not by huge margins and they won't be able to sustain that lead for more than a year or two more.