"I prefer" is simple present tense. When you say "I prefer" you are saying "I always like," because sentences in the simple present are habitual, or always true.
I would prefer (I'd prefer) is a conditional, and this means that your preference relies on something else. I'd prefer is often used with "rather than" or "over" or "to"
I prefer coffee over tea
I prefer coffee to tea
I prefer coffee rather than tea
Since prefer ALWAYS takes a gerund (-ing verb), your first sentence is correct.