I'm only just starting out with Rails too, but here are my thoughts...
Using inheritance in ordinary object-oriented languages gives you a
few benefits (and a few drawbacks!). Primarily, these are reuse and
If you are going to want to define a number of similar methods on
doctor and patient (including performing much of the same validation),
it may be worthwhile using inheritance. This way, you can write less
unit tests, and reduce duplication of code.
Furthermore, if you are likely to want to access all of the users in
the system, you can just iterate over Users rather than Doctors and
If you are interested in using inheritance, there are a number of ways
in which you can represent this relationship in your database. I would
recommend reading the relevant section in Agile Web Development with
Rails, if you have a copy of this book. And if you don't, I can't
recommend it highly enough; it's fantastic.
Hope this helps!