Recs.
Updated
SpecsUpdate
Pros
Pro Has nicely working, lightweight simulators for a lot of possible phones/tablets
You can launch a simulator for a specific model, it will start in seconds and will work as fast as a html page. If you want to see the result that you will get on another model or a tablet, you can pick the desired one from the list.
Pro Lightweight (specially regarding RAM) and fast
The RAM used is basically the same required for any other typical project in your IDE of choice. For example: using NetBeans, for a decently complex app it stays around 200-600MB, working perfectly within the bounds of 4GB RAM. The simulators run fast and are themselves lightweights.
Pro Allows full access to native OS code without sacrificing overall portability
Pro Doesn't require to learn the n-th new language and/or paradigm
The whole framework consists only of well documented java classes. No new language to learn, no new paradigm for coding. If you are used to code in Java, that's all you need. If you are a C++, C#, or even JavaScript programmer, once that you grasp the basic of Java, you are good.