Labelinfo.be offers a useful overview of sustainability labels. You can select lifestyle and clothing to limit the scope to those labels that are relevant to the fashion industry.
Each label is accompanied by its logo, a short description and a score based on three criteria: environment, social circumstances and assessment (reliability).
Labelinfo, an initiative of Netwerk Bewust Verbruiken (conscious consumer network), is a survival guide in times of label confusion.
Which certification system you ultimately use depends on what exactly you want prove. This guide on apparel and textile verification systems give you an overview and can help you decide (in Dutch).