I did one card per person (separate cards), my sister did one per couple. Both ways probably work, seeing as couples will be seated together, but I believe the proper way to do it is one card per person especially if escort cards are used for multiple purposes such as being gifts or indicating to staff the meal preference of the person if you are having a served meal.
ETA: lolo has a good point. I only had 40 guests so 40 escort cards was not a problem. If you have lots of guests, and you don't need one per guest, save yourself the trouble and just do one per couple.
Thanks all! I do have to indicate entree choices on the cards, so I guess I'll check in with my venue to see if it matters whether or not they know exactly what everyone got, or if it's fine to just know what each couple got like @lolo883.
I'm inviting 135...I guess that's not a TERRIBLE amount of cards if I do them all, but the idea of cutting that almost in half is enticing...
What differentiates an average host and a great host is anticipating unexpressed needs and wants of their guests. Just because the want/need is not expressed, doesn't mean it wouldn't be appreciated.
Re: Escort cards!
Plus I had 220 guests and the thought of 220 cards made me cry.