being on the hyperlite pro team, i have tons of experience with both of these boards. I started 14' season riding the franchise flex. its a ton of fun, very lightweight and thin board. I like it a lot for rails and air tricks, it holds its edge really well without fins. This is a faster shape. It does not offer the softest landings in the game tho, it lands a bit hard of the kicker compared to the union.
I got back on the union a few months ago and i will keep riding this board, its definitely my favorite. It has a ton of rocker, which helps tremendously with soft landings. Its got a ton of flex as well, great on rails. It will take a little more of an aggressive edge to release your air tricks, but you get a ton of pop off the flats. My recommendation for you is definitely the 142 union, you cannot go wrong here and the board will never break. Get systems too if your looking for extra soft landings! any more questions let me know!