Reviews Content Type with Rating Field We are looking to create a content type that will allow users to create reviews. Each review (node) when created it will be tagged with one taxonomy term. 

For example, any user can write a review for Phone > LG > G3 

One of the fields for the reviews content type will be RATING. The rating
will be five star and later will be used on a view to show an average score for the particular taxonomy term (product). 

Based on the example ablove show an average score for LG G3 phone. Which will be shown in a view. 

Should we use a list field (1,2,3,4,5 as options) for the RATING field? Or is better to wait until the Fivestar module is more mature? Haven't even used Fivestar but it seems that it will do what I am talking about. Or am I wrong?
Fivestar and maybe Rate seem like the modules for your problem. 

But you can also use a list field like you mention. You seem to have the need to restrict the voting to the author of the Review node, while creating it (on Node Edit, not to all visitors on Node View). 

But there aren't any ETA for Drupal 8 versions of those modules. Maybe you can help with that while working on your project? Although Fivestar has much more features than you seem to need, it's a more flexible solution and may be more future-proof. 

It all depends on when you need it working, and how much you can invest in getting the D8 versions up and running. 

If you're a developer or can sponsor one you can work on the D8 versions to get the superb usability for your users. 

If not you can use the List field and some Views magic to build the basic vote and stats structure.