I think you should take a chaplain or librarian based on what else is in the list. So a libby is a better choice with "foot sloggers" as he can use his force barrier. Whilst a chappy is better with a squad in LRC because they almost certain to get the charge allowing the awesome re-rolls. Personally I think that any sort of dedicated cc squad is overkill unless you plan to charge the opponents main cc unit (terminators, nobz etc). You should be able to wipe most units in 1 turn even with a shooty unit that has 1 pair of LC to help.*
If I were to go back to playing mech I would take a chaplain with a squad that looked something like: 1x sb/pw, 1x lc's, 1x ac/cf, 2x sb/pf. The unit still has good shooting capability and is rock hard in combat due to having a chaplain there. Then there's the lrc they cruise around in as well *
Shooty units again only need to take an AC and CF, perhaps an apothecary if you feel the need, but I'd never put both him and libby in the same squad. It leaves the other squads too vulnerable. Rather*keep them fairly close just incase.