First, it's important to note that cursive handwriting traditionally does have a slanted position. The tilted angle of the paper enables slanted letters. However, slanted writing is not a MUST for cursive. The Handwriting Without Tears program teaches and promotes an upright position of letters on the page.

What angle should cursive writing be?

The recommended slant angle is 55 degrees.

Is it better to write slant?

I always take lecture notes with an upright hand (more a semi-connected print than a completely cursive hand) because I find it so much easier to review or to find a particular point this way than with any kind of slanted hand. But when writing drafts, or scribbling performance notes, slant wins for its speed.