I think it's important to consider the differences in design between the synergy and superfeet. Superfeet are stiff all by themselves, in fact I run them in trail runners and muck boots because they add torsional ridgidity. In other words, they add stiffness to otherwise flexible soled footwear, and add a lot of support. If the green super feet feel to "hard" to you, it's worth considering the orange (women's equivalent are pink) which offer cushion in addition to the stiffness. Green superfeet have almost no cushion, but the orange/pink version have a considerable amount. I like the cushioned pink (orange) insoles in stiff footwear or when I pack a heavy load (I do summer backpack trips in saloman Speedcross trail runners with pink superfeet), and the green work well in softer soled shoes like sneakers/athletic shoes and rubber boots.
The synergy footbed is more like a gel insole, and doesn't offer anything in the way of torsional ridgidity that I can tell. But they are great in boots that already have a stiff sole. I have been running a pair in my Hanwag lady Alaskans for the last four seasons and they are still going strong. My Hanwags have a full shank, so I don't need additional stiffness from my insoles, just cushion and maybe the ability to reduce friction.
