It depends on your motivation for learning smart contract development.
If you want to be employable as soon as possible, or use the most widely supported language, and therefore the most documented and (relatively) stable tools, use Solidity. The frameworks, community, and resources will help get you up and running very quickly.
If you like to tinker with a language, and don't mind writing much simpler, but more auditable/secure smart contracts in a language WITHOUT the features, documentation, and community support that Solidity does, use Vyper.
In support of Vyper, a lot of the features that were stripped were in order to enhance auditability. You see, you should strive to make smart contracts as simple and readable as possible, because these contracts can't change, and minor flaws can spell financial disaster on a massive scale.
Here is a link to the Vyper Github for more information.
Here is a link to Solidity documentation.
Here is a good reddit post with more people discussing the merits of both Solidity and Vyper.