While Dustydog may have had a bad experience don't let that deter you from visiting any of the Scottish Islands.
You have to expect inclement weather in the north but as they say 'there is no such thing as bad weather, just poor clothing'!
I can't vouch for the scenery of the Outer Hebridies but would put the scenery of west coast Scotland and inner islands up against nearly anywhere.
If you are travelling in May/ June then I would suggest that is one of the best times to visit the Northern Isles - Orkney and Shetland. The weather tends to be dry, if not as warm as further south, and the long light nights are a new experience for many.
You can travel by ferry to both from Aberdeen, or take a more circular route via Scrabster to Orkney, onwards to Shetland, and returning via Aberdeen. This will cost about