When choosing influencers for your campaign, several key factors should be considered:

1. Relevance: Check if the influencer’s content aligns with your brand image and product. For instance, a fitness influencer would be a perfect match for a sports-oriented brand.

2. Reach: This is the number of followers the influencer has. Depending on your goals, you may opt for a macro-influencer (over 1 million followers), a mid-tier influencer (between 50,000 and 1 million followers), or a micro-influencer (1,000 – 50,000 followers).

3. Engagement Rate: An influencer with high engagement has a dedicated audience that comments, shares, and likes their content. This metric is critical to determining how active and influential an influencer is.

4. Audience Demographics: Consider the age, gender, location, etc., of the influencer’s audience. Ensure these align with your target market.

5. Quality of Content: Does the influencer produce high-quality, authentic content that resonates with their audience?

6. Costs: Different influencers charge different rates for sponsored content based on their reach and engagement rate. The influencer’s pricing should be within your budget.

Platforms like Flinque can be extremely useful in providing comprehensive and easy-to-understand audience analytics and facilitating influencer discovery. They offer advanced filters and comparative metrics to pinpoint the perfect influencers for your brand. However, each platform varies in terms of features and flexibility, so the selection should be based on your specific needs.

Remember, your choice of influencers will determine the effectiveness of your campaign, and hence a well-thought-out selection process is essential.