Forced, labored, strained, farfetched are comparable when they mean produced or kept up through effort and, therefore, neither natural nor easy nor spontaneous.
Forced is the widest in range of application of any of these terms, being referred not only to what is brought about by compulsion or to what is accomplished by exerting force beyond the usual limit, but also to what seems artificial because not natural, logical, or spontaneous or because constrained or affected.
Labored carries a stronger connotation of heaviness or of ponderousness or, sometimes, of tediousness as a result of great effort.
Strained adds to these an implication of tenseness or of a result that is unnaturally or distortedly labored.
Farfetched applies especially to an expression, an idea, an argument, or an explanation which has been carefully sought out so that it seems unduly strained and not quite naturally used.