Linseed oil is perhaps the best medium to use in oil painting, because it is simple and besides, linseed oil is usually part of the paint in the tube.
All drying oils -- whether used to grind pigments or used as painting mediums -- will eventually crack. Alkyd resins eventually crack. It is part of the aging process and is unavoidable. The only thing we can do is to use the best materials available, construct our paintings soundly and use rigid supports. If you use flexible supports, for example, your paintings will crack sooner than if you had painted on rigid supports. When using other substances besides oil as painting mediums to build your paintings, you are risking poor formulation, because that is what you are doing (paint formulating) when mixing other substances with oil colors. Few artists I know are good paint formulators. It is for this reason perhaps that we see so much inconsistency in the use of resins in artists' paint, although may resins, such as alkyds, have a good history of use in architectural and industrial paint. When incorrectly used, any paint material may cause problems, but when correctly used, as is evidenced in commercial paints, they provide benefits.