Mayonnaise is better than butter for sandwiches.
I find that mayonnaise is better for sandwiches than butter.
Mayonnaise also has a higher smoke point so when you're wanting to toast bread the mayonnaise is better than butter as it leads to more even browning of the bread.
Some people prefer the taste of butter on certain sandwiches but I prefer mayonnaise as many other people do as well.
Mayonnaise goes good in sandwiches as well and makes a sandwich taste so much better.
I use butter when I just want to eat a few slices of bread without anything else and make a toasted butter sandwich.
But when I add lettuce, meat etc I prefer to use mayonnaise when toasting the bread or when simply making a regular sandwich I like to add the mayonnaise inside the sandwich.
Mayonnaise also has a more neutral flavor profile which is also good when you want cheese and other fillings in the center to shine.
Mayonnaise is also a good substitute for butter when making grilled cheese sandwiches as they will come out nice and crispy.