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What are you looking for in a provider?

Locations, bandwidth, number of machines, orchestration capabilities, etc?

Avoiding lock in is 'easy'; avoid using specialized services and features that aren't universal. Avoid bundling services that need not be bundled. Your hosting provider should not also be your domain registrar, and maybe shouldn't be your DNS provider, nor your email provider. Big cloud has high outbound bandwidth rates, so avoid collecting a large amount of state that would need to be copied in a move. (Easier said than done)