Most people I know hate mayonnaise, but I love it on my burgers and sandwiches.  It's also a base to a lot of other things--like spinach dip.  I love me some good spinach dip!  It's also the base of the iconic McDonald's Big Mac sauce.  I'm not a fan of mustard by itself, but mixed with mayo, and slathered on a sandwich bun... yum yum get ya some!

For some reason just the smell of mustard makes my stomach turn. Mayo definitely FTW, though. I love putting it on sandwiches, subs, burgers, chips, hotdogs, chicken nuggets, wings and even pizza, which more than once has earned me hardcore "WTF?!" looks but honestly there are more things to worry about in the world than me putting mayo on a pizza... just saying.  

Both can kick rocks. I will not go near either. I use to work at a creamery and after that, i had to cross a few things off my list..    

Mustard 100% as I find mayo just detestable. Its not even a taste thing. I just think mayo is gross. That texture just makes me shudder. Completely irrational but meh what are you going to do?

I like both but tend to have and prefer Mayo more. Usually only use mustard when making Macaroni cheese.

depends on what it's on really mayo on a hotdog? no sir but mustard ketchup and relish on that hotdog? why yes please but generally mayo goes good on more foods than the mustard does

Definitely depends. Hotdog? Mustard all the way. Tuna sandwich? Mayo for sure. Hamburger? Has to have mayo but mustard is also okay here too. Potato salad? Miracle whip and mustard

I mostly use Mayo preferably but Mustard has its uses too, not only that their is some benefits to both:

• Mayonnaise is an excellent source of Vitamin K.

• Yellow mustard has more thiamin, riboflavin, niacin and Vitamin B6, however, mayonnaise contains more Vitamin B12.

• Yellow mustard is an excellent source of calcium and dietary fiber.

I am a big garlic mayo fan, but mustard is something i have never enjoyed.    A chilli sauce, maybe a picalilly or some branston pickle with a ham sandwich but never mustard.   If i was told i am stuck on a dessert island with just mustard, i will wilt away quickly

I love mayo on my sandwiches or in my tuna mayo. Not much of a mustard person as it tastes so weird

mayo is the best. with ketchup its even better! mustard cant be tasty with ketchup at all

Mayo all the way, even like it mixed with tomato sauce. American mustard is alright on burgers and hotdogs, English mustard isn't really nice for anything.

I love me some mayo on my fries.  It's even amazing on burgers! omg I am now craving burgers and fries.... why have you forsaken me with this question!

I think these champs both deserve a place in your refrigerator. Both also are very good as basis for all kinds of sauces by the way, worth checking out.

I use Mayo always, but sometimes I use both. 

I like both, but really depends on what I am eating or using either for.  Some recipes require both, so that makes it easy to decide which I like best. ;)