I lived in Shetland for 12 years. Roro Ferry from Aberdeen (Northlink) is overnight and you’ll want a cabin. It’s pretty pricey and gets booked up quickly in the summer. Great roads for motorbiking if the weather and wind are kind and easy access to a number of islands on roro ferries. Accomodation can be hard to find at short notice in the summer and pricey. Not a massive amount of cafes when you’re out an about. I loved it there but we needed to be more accessible to family who weren’t there so moved to mainland Scotland.
Orkney is great too. Easier and cheaper to get to with a ferry from Roro Aberdeen (Northlink) or ferries from Scrabster area. Some of the other isles take a bit more planning and time to get to. More accommodation and more cafes etc than shetland and a different landscape than shetland too with much more obvious farming and cows. The west coast of Orkney and Hoy (Rackwick and the old man) are my favourite areas, but if you’ve never been before it’s all great.
Both places can get very wild and windy and there’s not much shelter from it.