General:
* Vanguard
* Leading edge
* Cutting edge
* Head
* Front ranks
* First line
* Foremost
* Prominent
* Preeminent
* Leading
Emphasis on importance:
* Crucial
* Central
* Key
* Essential
* Primary
Emphasis on position:
* Front
* Top
* Summit
* Apex
Emphasis on innovation:
* Pioneering
* Groundbreaking
* Trailblazing
* Innovative
Emphasis on visibility:
* Notable
* Eminent
* Distinguished
* Prominent
The best synonym will depend on the specific context of your sentence. For example, if you're talking about a company at the forefront of technology, "cutting edge" or "leading edge" might be appropriate. If you're talking about a person who is at the forefront of a movement, "prominent" or "leading" might be better choices.