Take your fashion cues from the bride. It's the wedding dress that determines what style of attire the mother of the groom or mother of the bride should wear.
If the bride is wearing a traditional wedding gown with a long train, the Mother of The Bride and the Mother of the Groom should also wear formal dresses for such a special occasion. Many brides today wear strapless wedding dresses. Mothers of the Bride and Groom who don't want to bare it all can wear a strapless gown with a shawl or jacket. If the bride is wearing a tailored suit or short dress, the mothers can take their cue and wear a dress that's short or a suit with a short skirt. Also consider the time and place of the wedding and any dress code that will appear on the invitation to guide what guests should wear such as Black Tie.
Mothers of the Bride and Groom should consult with the Bride before they go shopping for their dresses. The bride, your daughter or future daughter-in-Law, may want you to wear a particular color or shade. If the bride leaves the color up to you, select a color that coordinates with the dresses worn by the bridesmaids. For example, if the bridesmaids are wearing pink, the Mothers might select a dress in shades of rose, But it doesn't have to match. Ultimately, it's best to select a color and style that looks best on you because It flatters your figure, your skin, and hair tones.