Google Ads are a great place to start advertising if you aren't on the first page of Google's search engine for your niche. Simple text based ads that are extremely specific to a niche.
Facebook ads are versitile and effective. You can run text, images or video. Highly graphic and engaging video ads are very effective on Facebook. Cross-platform capabilities with Instagram are also effective.
Similar to Facebook, Instagram is highly visual. Althought the demographics of Instagram are a bit different. Instagram is mobile first and can target your niche very specifically.
LinkedIn is a great place to curate B2B relationships. In addition, the mindset of LinkedIn users is motivated to professional services. B2B advertising is very effective on LinkedIn.
Video marketing is one of the most powerful forms of advertising. YouTube's best in-class algorythm means the right ad is going to be in front of the right person at the right time.
Reddit, be design, is built around segmentation. As a result, finding the right audience for your ad can be simpler to do on this platform. Ads on Reddit are effective in both text and video based advertisements.