As far as the scope is concerned both have a wide scope. Every business needs a website, so web development is an essential skill. Though mobile apps have earned millions too. Like uber, zomato etc.
Pros of learning web development:
Easy to learn
Demand.
You will not be jobless if you know this skill.
4. Sometimes you could just download templates and make use of them without much effort.
5 Through ionic and phonegap-like frameworks you can convert website into mobile app. ( But still, you need to understand the basics of mobile development)
Cons:
1 As it is easy to learn so there is a tough competition for web developers.
2 Price paid per web app is relatively less than mob development.
Pros of Android development
Lot of community support in learning.(Backed up by google)
Demand.
Android has a huge worldwide market and the most used mobile platform is android.
Libraries available to decrease efforts.
Cons:
1. No client demands only an Android app. They also require an ios app if they are targeting mobile users.
2. You need to understand the basics of java first.
We pay to milkmen because they provide us milk.
We pay to shopkeeper because they provide us with some product
We pay for train tickets because they take us from one place to another easily and save our time.
Nobody is going to pay you to create a web app or Android app. People will pay you for the value you provide to them.......