Late May it's a good time for the West Highlands, we often have good weather it's slightly quieter than once the kids have broken up at the end of June here. Rhododendrons and gorse bushes are in full bloom looking glorious and the gorse smells amazing on the breeze. For midge repellent I highly recommend Mary Jean midge lotion. It's all natural, has a pleasant smell, is kind to the skin and it works! I don't know if it's sold in any of the shops, I get mine online.
September is also good because it's usually still warm & you have such lovely colour all around with the leaves turning. Depends what you're looking for really