All spouses provide gold, food, and the Lover's Comfort buff (unless they may also double as a follower). It's surprising how many people don't know that. Yes, some spouses already own houses and businesses but that doesn't necessarily make them better, or more beneficial spouses. Honestly, they all offer the same benefits with no one having an advantage over the other. All provide 100 gold per day, but sometimes they may give more (at random). Investing in their business can help increase this return.
Be wary though of "warrior spouses", most NPCs will lose their essential status after marriage making them able to die. You'll lose a valuable follower and your husband/wife. The only exception is Mjoll, as mentioned above. For some reason she is one of the only marriage eligible spouses that remains essential afterward.