It is not a compatitor to inflation - two different animals.
String theory is kind of Unified Field theory - what all stuff around us (electrons,protons, photons, gravitons, etc) could be made of. String hypothesis (it is still in hypothetical state because there are no experimental facts to verify or disprove it yet) proposes to consider everything as multidimensional loops (manifolds) of massless space itself vibrating with the speed of light at various certain frequencies (like harmonics), and the energy levels of those vibrations are what we call masses of various elementary particles we see around - proton, electron, photon, etc: m=hf/c^2. Loops (manifolds) are presumed to be of Plank size (10^-35 m) or close to that. And because of the small scale of Plank size, and lack of any microscope of that magnification (best particle accelerators can probe 10^-18 m only) there is a problem to retreive information about events on that small scale from 10^17 order more rough measurements, and thus no experimental evidenses to support/ disprove string hypothesis are around yet.
Inflation theory seems to be on much furmer ground, as there are a few experimental evidenses which it fits (see my previous post). And actually it is not a theory, but a constatation of fact that space could not expand steadily to explain what we have now - it HAS to inflate in the past.
WHAT might cause that inflation - another story (there are several candidate theories like false vacuum transition, space-time fluctuation, antigravity, negative energy, spur from another previousely existed universe, collision of previous universes, etc., - all in hypothetical state yet).
So, these are 2 different theories (inflation and strings).
Although if sring model can be proven, then as one of the tests it should pass, it should accurately predict/ explain the inflation of space during history of early Universe.