Learn Spanish (Latin America): ¿Tú prefieres un plan diferente?

The verb is preferir (to prefer). It is a "stem-changing" verb, which means the vowel in the middle changes when you use it. For preferir, the second e changes to ie in most forms, including the tú (you) form. So, prefer- becomes prefier-, giving us prefieres.

Since preferir is an -ir verb, why does it end in -es instead of "-is"?

In the present tense, regular -er and -ir verbs share almost the exact same endings. For the tú (you informal) form, both end in -es (like comes and escribes). The main difference between -er and -ir verbs happens in the nosotros (we) form, which would be preferimos.

Do I have to include tú at the beginning of the question?

No, it is completely optional. Because the verb prefieres already tells us who the subject is (you), the word tú isn't strictly necessary. However, native speakers often include it in questions to sound a bit friendlier or to add emphasis.

Why does diferente come after plan?