If you eat it meat is an excellent source of protein while contributing very little carbohydrates to your life. It also relatively easy to add to any meal. But which source is better? . As with most things, each source has its own pros and cons and a lot of it comes down to personal preference. Featured here is sirloin steak, chicken fillet, salmon fillet, with the numbers quotes for 100g. As you can see the chicken is the leanest, while steak offers the highest volume of protein. Salmon then has an excellent micronutrient profile - for example being source of omega 3s. .
Of course then it comes down to what you LIKE, what meal you want to add it to etc. Meaning there probably is no 'Best'. I know for me, I have no preference, and will eat combination of all three.