- If I have to choose a Ruby tech, I would go for Rails, no Sinatra, no Padrino, nop. Whatever you think is simple now it will change in the future. So start with what you know well and has everything you might need, even if you're not using it now. I've seen many "small" services being rewritten in Rails for this reason and that's painful and a waste of resources.

- Nowadays I have several reasons not to use Rails for new projects (https://blog.jaredfriedman.com/2015/09/15/why-i-wouldnt-use-...). But I actually I have more reasons to use Elixir instead (https://medium.com/@kenmazaika/why-im-betting-on-elixir-7c8f...) (http://blog.carbonfive.com/2016/04/19/elixir-and-phoenix-the...). And yes, it's fun, incredibly robust and scalable. :D