The more promising player is… Joe Flacco
Say what you want about Joe Flacco he has been a rock for the Ravens organization. He almost made it 11 full seasons as the starting quarterback for a reason. While he never lived up to the enormous contract he got himself, Flacco was always a viable starter in the NFL. Flacco is more of a sure thing than Foles. At their peak, neither player is much more impressive than the other. The larger wealth of experience makes Flacco a more sensible pick for a team that has their druthers.
Joe Flacco has worked with a plethora of offensive coordinators while Foles has only had success with Andy Reid or his protege Doug Pederson. Flacco has made it work with Cam Cameron, Jim Caldwell, Gary Kubiak and to some extent Marty Mornhinweg (nothing really worked with Marc Trestman). If you have to put these two quarterbacks in completely different circumstances, Flacco is the best bet.
There is a very good chance that both of these players are playing for a new team in 2019. The Ravens are moving on from the Flacco era while the Eagles are moving forward with Carson Wentz. They should be both available players. It will be fun to see where they go.