Unity Plugin or Unity in Android SDK.

Hey guys, need a point in the right direction using Unity Android. I am looking to use some Android Java code I have and was wondering the best way to go about things. I have managed to integrate unity with eclipse. I have also managed to get a very basic Java plugin working in Unity using C++.

I am still learning and do not comprehend a lot of it and want to know which one to focus on and will suit my needs best.

I will be looking initially to do some simple things, but eventually would like to do things like accessing the facebook graph api from the application. (I realise there are plugins for sale for this, but am doing this for learning)

With that in mind, am I better off using Java C++ plugins in Unity or getting my unity scenes running in eclipse and the android sdk? Is it possible both ways? What are the positives and negatives?

Thanks.