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If you already have some programming knowledge, then go for whichever is close to your field. Otherwise choose the one depending on your interests. The Android has an advantage that you can show your work to your friends and they can use it in their day to day lives. In web development, you have to work as a freelancer to promote your work and skills. But you can publish your own Android apps. Android is not everything, you may need to learn iOS and Windows to release your apps on all platforms. But you can distribute your website among wide variety of target audience (depends on the language). You should plan your product type and then choose the medium.
Which languages do you master?