EF Code First vs Database First?

Code-first Vs Database-first

• You did SQL DB Admin before - you probably know something about DB and how to design them for a performance - EF will not do anything from this for you. EF will not create indexes for you etc.
• 30-40 tables means that you will not build the model in one shoot. You will start with the small model and continuously grow it. Once you start making changes in DB or adding initialization data you will not want to lose these changes and the data. Code-first allows only deleting the whole database and recreating it from scratch. Model-first allow building the DB incrementally but you need Entity Designer Database Generation Power pack and VS 2010 Premium or Ultimate ($5.000-$10.000).

CodeFirst cannot do anything that DB first cannot. At the end of the day they are both using the Entity Framework.

The main advantages of using codefirst are:

• Development Speed - You do not have to worry about creating a DB you just start coding. Good for developers coming from a programming background without much DBA experience. It also has automatic database updates so whenever you model changes the DB is also automatically updated.
• POCOs - The code is a lot cleaner you do not end up with loads of auto-generated code. You have full control of each of your classes.
• Simple - you do not have a edmx model to update or maintain

For more info see Code-first vs Model/Database-first and here Code-First or Database-First, how to choose?

Both are good it depends on your requirement only.  No one can say one is good other is not.  

I think the differences are:

Code first

• Very popular because hardcore programmers don't like any kind of designers and defining mapping in EDMX xml is too complex.
• Full control over the code (no autogenerated code which is hard to modify).
• General expectation is that you do not bother with DB. DB is just a storage with no logic. EF will handle creation and you don't want to know how it do the job.
• Manual changes to database will be most probably lost because your code defines the database.

Database first

• Very popular if you have DB designed by DBAs, developed separately or if you have existing DB.
• You will let EF create entities for you and after modification of mapping you will generate POCO entities.
• If you want additional features in POCO entities you must either T4 modify template or use partial classes.
• Manual changes to the database are possible because the database defines your domain model. You can always update model from database (this feature works quite good).
• I often use this together VS Database projects (only Premium and Ultimate version).

If your database is ready then go to DB first approach it will create all the classes automatically      

If you are new in EF then I will recommend DB first approach. It will easy and simple to use without much configuration. Anyone start to learn FE they should go with EF after having clear idea about that you can go with code first approach so it will be easier.   

It depends on your requirement if you want full control through c# code then use code first approach otherwise DB first.