I would not look for one “best” AI video tool, because they are good for different tasks.
Runway — paid/freemium. Probably one of the best if you want more cinematic or polished AI video.
Pika — free + paid. Very easy to start with, good for short clips, effects and social media style videos.
Luma Dream Machine — free trial credits + paid. Good for realistic short scenes and quick image-to-video tests.
Kling AI — freemium/paid. Strong for image-to-video, motion and character consistency.
CapCut AI Video Generator — free/freemium. Not the most advanced cinematic generator, but very useful if you need quick TikTok/Reels/Shorts content with templates, voiceover and editing in one place.