Proper or optimized test way within asp.net web api application

We have an asp.net web api application, in which we used this architecture:

1. Presentation Layer

2. BLL layer

3. Dal Layer

We discussed, me and my colleges, about TDD and how can we used it in our project :

My Approach

I see that we have to test the BLL layer by adding full unit tests list, Then we test the presentation layer

Other opinion

We have only to test the services(presentation layer). If a test failed then, we test only the methods(in bll) which have relation with this service

So the discussion is about

Proper vs optimized way

So I need to know

1. What is the best approach between them?
2. Can the size and the type of the project interfers in this comparison?

Thanks,