Sounds like you might benifit from this video. Andrew talks of a traffic light system, and going with a high competition to me sounds slightly dangerous because the more competition there is, the harder it is to be picked out of the competition by the viewer. If your thumbnail isn't as good as others, you may rank high for a highly competitive keyword, but someone else's video might perform better for that keyword simply for having a better thumbnail. If 1 million people make a video about dogs, it's going to be hard to be the best out of 1 million videos. But if there's only 10 videos that cover a topic, you have much better chance of ranking for it. I'm still not that well versed in terms of optimization so this will be something for me to learn as well, but from my understanding, you want to be very careful targeting high competition keywords.
View: https://www.youtube.com/watch?v=qoEh7qwQbNc