I think that if they are planning to make X-Men films they should cast the original actors/actress. New faces will be little bit weird. It would be like Blues Clues remember what happened to Blues Clues. hahaha Steve will always be the best.
For me the original cast did a great job it was just the writing which they had to follow. But if they are planning to cast younger versions of the cast then its fine. As long as they still look good on screen.
Original cast made my whole X-men experience.