Both have the Female leads with the dream of becoming a voice actress.
Both shows also have a romance elements if that is what your looking for as well.
Both shows are comedy, but they also have a touch of drama.
The difference really is the length REC (9 episodes including a special) and Love Get Chu (25 Episodes).
So if you in it for the long haul go with Love Chu, but if you want something short and sweet with a touch of Drama REC is the way to go.
Both of these shows follow a group of girls as they progress in their desired career in show business. Love Get Chu's characters are aiming to be seiyuu but later also become idols, and iM@S' characters are aiming to become idols of course. Focus is given in both shows to the effort that the characters put into their work in order to make others happy.
in girls high, there is one girl who aspires to be an actress, while in love get chu, 5 girls aspires to become voice actresses, and also green haired, glasses wearing girls, rinka suzuki and ayano sato