In both settings, they are both perfect for Indy.
River was far more serious, a distinguised actor well known for previous works and had the manner of Harrison Ford to introuce the audiences of 1989 to a rugged young Indy read for action and adventure...leading perfectly into TLC, as also showing us the (forgive me!) somewhat convienent order of Indy hating snakes, using a whip and getting his scar AND obtaining his hat all in the space of 10 minutes! Perfect incarnation.
But no-one could pull of a more world aware and naive young Indy than Flanery, we saw a more human character there able to travel the globe and feel the pangs of love, loss, awe and inspiration over the years to show the development of Indy's knowledge and interest in what he does now, 20 years on.
They both fit the bill perfectly, and for Flanery being a lesser known actor as Indy, I feel I can accept him as nothing BUT Indy and follow him through the adventures whilst learning about him in a way I probably couldn't with River, being a more distinguished actor and his Indy range only stretching about 20-30 minutes.
Nice work from both who created Young Indy perfectly in their given media.