I think Leoppold might have been a better choice for a number of reasons. First he seems to have had at least less obviously extravagant tastes than Otto did, and his religious tempraments might have made him more amenable to the Greek people. While he himself might not have converted to Orthodoxy, had he married an Orthodox wife (Though the 35 year age gap would be tough the Russian princess Alexandra Nikolovena might be a fit, or a junior princess of the Romanov line which might also help placate the pro-Russian branch of the Greek political system) and their child been baptised ORthodox it might have served to further unite the country. I also think Leopold was a bit more shrewd than Otto and might have avoided the embarrasing blockade of 1850 and 1853, though Greece might well have been saked to avoid the Crimean war altogether regardless. Avoiding the absolutism might also lead to waning power of the "outsiders" and might open the door for somehow bringing Crete, Thessaly, and/or the Ionian islands under Greek control much earlier.