He chose it because it was well balanced in the hand.

Then they sallied out into Cornhill, past the Exchange, erected by the worshipful citizen Sir Thomas Gresham, and then into Chepeside, where they were astonished at the wealth and variety of the wares displayed in the shops.

Gazing into the windows, they frequently got into the way, and were saluted many times with the query, "Where are you going, stupids ?" a question which Hugh was largely inclined to resent, and would have done so had not Rupert told him that evidently they did get into the way of the hurrying citizens, and that it was more wise to put up with rudeness than to embark in a series of quarrels, in which, moreover, as strangers they were likely to get the worst of the dispute.

Saint Paul's Cathedral, then but newly finished, astonished them vastly with its size and magnificence, and they returned to the midday dinner at the Bell delighted with all that they had seen.
Asking the landlord how he would recommend them to pass the afternoon, he said that they could do no better than take a boat at London Bridge, and be rowed up to the village of Chelsea, where many of the nobility did dwell, and then coming back to Westminster might get out there, see the Abbey and the great Hall, and then walk back along the Strand.
The lads followed the advice, and were soon delighted and surprised with the great river, then pure and limpid, and covered with boats proceeding rapidly in all directions, for it was at that time the great highway of London.

Tide was flowing and the river nearly full, and having given their waterman the intimation that time did not press, he rowed them very gently along in the centre of the stream, pointing out to them, when they had passed above the limits of the city, the various noblemen's houses scattered along the banks of the river.