You will enjoy the 150/2.8. Very sharp and affordable. A no-brainer. It is wide enough to step back and get some air around the subject but you can get close too and fill the frame with head & shoulders. If you want nose-hairs & pores, it'll be the 165/2.8.

Consider the 165/4 LS if you want to use flash, as it is a leaf shutter lens and will sync at a variety of speeds.

Any one doing a lot of portrait work would be justified having all three.