High temperature water is great for removing hard stains and you may often combine it with bleach to get whites very clean.

High temperature water can be detrimental to some fabrics and is likely to wash away some dyes over time.

Typically white cotton blends are the best for high temp washing.
Hand washing is time consuming and can be a labor-intensive option but sometimes it’s necessary for specialty fabrics like velvets, silks or very thin synthetic blends.

It’s fairly rare that hand washing is required for underwear but occasionally the designer / manufacturer will recommend it for their items.
Delicate detergents may not be as effective as regular detergents for more dirty items but they will be less harsh on the fabric finish and color when used in a wash.

Often delicate detergents are more expensive.

For specialty fabric and color underwear items this may be a good option to enhance longevity.
Some regular detergents can be great for removing stains and dirt but they can be harsher on the fabric finish, colors as well as the construction of an underwear item.

Garments that can hold up to regular detergents will typically be all-day wear made from mainstream cotton blends or microfibers.
For specialty items with unique fabrics and more delicate construction you’ll want to line or air dry them after washing.

Certain synthetic fabrics will melt under high-heat machine drying and air drying is your only option to prevent your garment from degrading prematurely.
Machine drying is one of the most harsh things to put your garments through and will lead to degradation of elastics and certain fabrics over time.

Speaking realistically, you’ll want the majority of your underwear to hold up to machine drying.
No hand-washing required and regular agitation and spin drying in a regular washing machine will be fine for these underwear items.

Typically you won’t have to worry about mixing different types of garments in the wash with your machine washable underwear.