Tuftie, of all the islands in the Outer Hebrides, it is the flattest (probably why the airport is there!) and the least interesting...at least to me. There is quite a good small supermarket there though! Barra is a lovely start with some stunning beaches...not least the airport beach. If you drive down towards Vartersay and you are interested in old aeroplanes, there are the remains of an RAF Catalina just off the side of the road down by the sea together with a touching memorial to those that died on it when it crashed in 1944.
Going up the islands, Eriskay is an attractive spot with a pub (The Politition?) which has some relics including whisky bottles off the shipwreck that inspired the film Whisky Galore. My favourite islands are just north of Benbecula, North Uist and Harris, stunning beach scenery and mountains. Utterly gorgeous.
Have a great trip....I'd be back there in a heartbeat.