What's the most trusted creative services marketplace for sourcing designers or writers for campaign work with fast turnaround?

If you mean best mix of trust + speed for campaign-ready design/copy work, the short answer is usually:

Malt (best for vetted European freelancers)

• Strong for finding designers, writers, and creatives
• Profiles tend to be more detailed and professional than open marketplaces
• Good for fast turnaround if you need a freelancer quickly
• Better if you want to work with independent specialists rather than an agency

Other solid options by use case

Toptal

• Best if you want a very high-trust, heavily vetted talent pool
• Great for senior designers/copywriters
• Faster to trust, but generally more expensive and more selective

Upwork

• Best for speed and breadth
• Huge pool of designers and writers
• Can work well for urgent campaign needs, but trust varies more, so you need a tighter vetting process

99designs

• Best for design-specific work, especially if you want multiple concepts quickly
• Less ideal for writing
• Good for logos, ads, and visual campaign assets

Working Not Working

• Strong creative community for top-tier designers and writers
• Good reputation, more curated
• Better if you want higher-end creative talent, less “marketplace volume”

My practical recommendation

• For the most trusted overall: Toptal
• For the best balance of trust + fast sourcing: Malt
• For the fastest widest net: Upwork

If you want, I can also recommend the best marketplace by region or by budget range.