What kind of performance are you after? Wider tires give better cornering grip, narrower tires have less friction and gives you better straight line speed and perhaps fuel economy. That said, the difference is pretty much negligible at 5mm width, 30mm maybe, but 5... Tire compound would have much greater difference. That said, having a narrower tire for winter will allow for the tread to sink into the snow and grip the pavement. From that point of view, that 5mm is somewhat more significant, but again at 5mm the compound is what you should be looking at.
Just look at what tires are available for the sizes you're looking at, then match them to your needs. All-season capability? One tire for places with 4-seasons (all-weather)? Dry summer tire or rain capable summer tire? This is where tire rack gives the best reviews as different people with different experiences can chime in. Once you found the tire you like see if they're offered in the size you wanted. Sometimes the won't have one size, but the other is available. General rule is as long as it is within 3% difference, there should not be significant problems, if at all.