Really rate the Surly Bill due to the hitch which loads both sides of the dropouts and due to the low pivot point any side loads are applied close to the ground plane, reducing the force pushing the bike over. It is a great trailer to tow and doesn't introduce any handling anomalies unless you've loaded it somewhere over 40 or 50kg. It is probably more awkward to manouver by hand than the Donkey (which I haven't used) due to the hitch though. In my experience of the BOB I would avoid a single wheel trailer for any regular load over 20kg due to the handling.
Really rate the Surly Bill due to the hitch which loads both sides of the dropouts and due to the low pivot point any side loads are applied close to the ground plane, reducing the force pushing the bike over. It is a great trailer to tow and doesn't introduce any handling anomalies unless you've loaded it somewhere over 40 or 50kg. It is probably more awkward to manouver by hand than the Donkey (which I haven't used) due to the hitch though. In my experience of the BOB I would avoid a single wheel trailer for any regular load over 20kg due to the handling.