The short answer is, probably strawberry blonde. There are some unusual factors to consider here.
Red hair is not actually a recessive gene (like blonde is), but is rather an "incomplete dominant." In the world of genes, there are dominant genes, which take over any recessive gene (brown, black), recessive genes (blonde), which will be taken over by any dominant gene, or incomplete dominent genes (red). Incomplete dominant genes will "blend" with any dominant, recessive or other incomplete dominant gene. I, for example, have "auburn" hair, which is essentially red blended with brown. Strawberry blondes are red blended with blonde.
So you've got yourself a red headed parent (let's call those genes aa) and a blonde parent, which we'll represent as bb. 100% of the offspring will have one hair color gene from each parent, or ab. This means red and blonde. Since red will always blend with other genes, the resulting hair color should be a blend of blonde and red, or strawberry blonde. In the case of my parents, which both have brown hair (let's call the brown/black genes C), either one parent or possibly both are carrying one "a" in addition to their brown or black genes, with the possibility of even a blonde thrown in (CC, Cb, or Ca). My parents are probably (Ca, CC). I'm probably a Ca, or a blend of brown and red. This result has an outcome likelihood of 50%.