Every product manager has opinions about product and roadmap prioritization.  As an industry we run the gamut from subjective to objective decision making.  I've seen product managers who fly completely by the seat of their pants,I've seen PMs who poll everyone on their team, I've seen PMs that let the business dictate what to build, and I've seen PMs who refuse to build any feature they don't have hard evidence necessitating.

So while there are a lot of methodologies out there (the Value vs Complexity matrix being a particular favorite with lots and lots and lots and lots of articles about it) I prefer a prioritization matrix with more than two axes.  For any product you have a number of subjective fields: executive priority for one, customer priority for another, your engineering team's priority for yet another.  These priorities don't have any objective values attached to them.  So instead of guessing or ignoring those priorities, let's assign a weight to them (1-10).  For each feature you can then simply add up the values and see what people really care about.  

A process like this shouldn't replace your judgement as a product manager, but it's a great tool that can help guide you to making the right decision.  Ultimately, by assigning some objectivity to a subjective process you can help reduce planning errors and increase the surety with which you plan your product roadmaps!