Of the three lakes on the western side of the Lake District, Ullswater is definitely the one Goldilocks would choose. Windermere is too big, brash and busy. Coniston is a bit of a wild, windswept wasteland.
Ullswater, on the other-hand is just right. It is the second largest lake in the area, has facilities for quiet water sports, a small fleet of 'steamers' and plenty of other things to see and do.
It also claims to be the most beautiful of the lakes. I wouldn't disagree with that.
It is also quite the best way to approach the Lake District. At its northern end the land is relatively flat and pastoral. At its southern end, the glacial valley continues on past Brother's Water to the Kirkstone Pass, the highest road pass in the area.