How would you rate each of them in terms of:
I like my SQL and so have always been a die-hard fan of ADO.NET and stored procedures but I recently had a play with Linq to SQL and was blown away by how quickly I was writing out my DataAccess layer and have decided to spend some time really understanding either Linq to SQL or EF... or neither?
I just want to check, that there isn't a great flaw in any of these technologies that would render my research time useless. E.g. performance is terrible, it's cool for simple apps but can only take you so far.
Update: Can you concentrate on EF VS L2S VS SPs rather than ORM VS SPs. I'm mainly interested by EF VS L2S. But am keen to have them compared against stored procs too since plain SQl is something I know a lot about.
First off, if you're starting a new project, go with Entity Framework ("EF") - it now generates much better SQL (more like Linq to SQL does) and is easier to maintain and more powerful than Linq to SQL ("L2S"). As of the release of .NET 4.0, I consider Linq to SQL to be an obsolete technology. MS has been very open about not continuing L2S development further.
This is tricky to answer. For most single-entity operations (CRUD) you will find just about equivalent performance with all three technologies. You do have to know how EF and Linq to SQL work in order to use them to their fullest. For high-volume operations like polling queries, you may want to have EF/L2S "compile" your entity query such that the framework doesn't have to constantly regenerate the SQL, or you can run into scalability issues. (see edits)
For bulk updates where you're updating massive amounts of data, raw SQL or a stored procedure will always perform better than an ORM solution because you don't have to marshal the data over the wire to the ORM to perform updates.
2) Speed of Development
In most scenarios, EF will blow away naked SQL/stored procs when it comes to speed of development. The EF designer can update your model from your database as it changes (upon request), so you don't run into synchronization issues between your object code and your database code. The only time I would not consider using an ORM is when you're doing a reporting/dashboard type application where you aren't doing any updating, or when you're creating an application just to do raw data maintenance operations on a database.
3) Neat/Maintainable code
Hands down, EF beats SQL/sprocs. Because your relationships are modeled, joins in your code are relatively infrequent. The relationships of the entities are almost self-evident to the reader for most queries. Nothing is worse than having to go from tier to tier debugging or through multiple SQL/middle tier in order to understand what's actually happening to your data. EF brings your data model into your code in a very powerful way.
Stored procs and raw SQL are more "flexible". You can leverage sprocs and SQL to generate faster queries for the odd specific case, and you can leverage native DB functionality easier than you can with and ORM.
Don't get caught up in the false dichotomy of choosing an ORM vs using stored procedures. You can use both in the same application, and you probably should. Big bulk operations should go in stored procedures or SQL (which can actually be called by the EF), and EF should be used for your CRUD operations and most of your middle-tier's needs. Perhaps you'd choose to use SQL for writing your reports. I guess the moral of the story is the same as it's always been. Use the right tool for the job. But the skinny of it is, EF is very good nowadays (as of .NET 4.0). Spend some real time reading and understanding it in depth and you can create some amazing, high-performance apps with ease.
EDIT: EF 5 simplifies this part a bit with auto-compiled LINQ Queries, but for real high volume stuff, you'll definitely need to test and analyze what fits best for you in the real world.
The general tradeoff is between having a great flexibility and losing lots of time vs. being restricted in what you can do but having it done very quickly.
There is no general answer to this question. It's a matter of holy wars. Also depends on a project at hand and your needs. Pick up what works best for you.