what is the best blockchain ?

This is not an easy answer and as usual it depends...on the following factors 

I call it the Blockchain Playbook: 

1. Scalability 
2. Security 
3. Decentralization 
4. Gas Fees
5. Developer Tools & Community 
6. Audience

The first three usually describe a triangular relationship. None of these go w/o sacrificing at least one of the other. Scalability basically means: can your blockchain of choice service millions of users at the same time? Or is it dead-slow like proof-of-work consensus algorithms like Blockchain or Ethereum. Decentralization means: how many independent validators does a blockchain operate ? Is it  100k like BTC or 7000 like ETH, which makes both networks almost impossible to hack, hence provide a higher security. If you want to have highly scalable blockchains that are able to serve 100k TPS, this will come at the expense of lowering security and decentralization. 

The more congested a network and the more nodes needed to validate a transaction the higher the gas fees (transaction fees). High gas fees obviously will have a negative impact on frequent usage and average transactions per user. 

Developer Tools and Community are an important driver as it is necessary to rely on existing developer tools to reduce cycle time and have a community from which you can hire engineers. Since Solidity is the language of Ethereum smart contract it is advisable to rely on languages close to that so that developers can quickly adopt the operating framework in place. If the overall eco-system in terms of vertical overlap is high, it will be easier to collaborate with other companies in the domain, solve difficult problems and exchange knowledge. 

Audience. The higher the existing audience the higher the adoption and conversion rate. Usually, higher audiences indicate that user-facing front-end tools such as wallets already enjoy a high penetration and users do not have to fill their wallets with unknown currencies or tokens previously unknown to them.