How to maximize SEO of an internationalized website

Question

I am creating a website with multi languages

I wish to get as much SEO as possible 

I have these alternatives:

Alternative 1: Separate domains

http://www.example.com -- English for default
http://www.example.com.fr
http://www.example.com.es
http://www.example.com.it

Alternative 2: Sub domains

http://www.example.com -- English for default
http://fr.example.com
http://es.example.com
http://it.example.com

Alternative 3: Sub folders

http://www.example.com -- English for default
http://www.example.com/fr
http://www.example.com/es
http://www.example.com/it

Answer 1

there is no single answer to SEO analysis  its unique based on the website, the market , the brand  i can list out some good possible URL structures

Separate domain

Sub domains

Sub folders