For engagement portraits, I think choosing a meaningful location is better, rather than a portrait studio. Choose a location that is meaningful to you, like the place you met or someplace you like to spend time together.
I would recommend to choose a season different from your wedding. If you have a Fall wedding planned, perhaps a Spring engagement session would be nice. Also plan ahead for what the images will be used for. For example; if you want to use them for "Save the Date" announcements, make sure you have them done early enough. Or if you are going to use them to include in a Love Story slideshow for your engagement party or reception, allow enough time to have the slideshow created in time.
Couples have many purposes for choosing to have an engagement portrait done. Many like to have a professional portrait presented on the signing table at the reception. Some need a photo for a newspaper announcement or for "Save the Date" announcements. The engagement portrait is also a great way for you and your photographer to get to know one another. That way you have an idea of what to expect on the wedding day.