It depends. If you come from a visual design background, then UI designer would be your best choice. Although, the market is looking for designers with the proper design process + years of experience and visual design skills. Ultimately, companies want someone who can start on the first day of work without any trouble.
User research: this role is heavily focused on utilizing the right research methodologies to gather the right information that the team will need to help influence the design decisions.
UX Designer: this role encompasses both research and design responsibilities, but may differ from bigger companies where you may be more focused in one area.
UI Designer: responsible for making the product visually appealing with fun, creative and delightful interactions.