I run the Tunze osmolator and an Apex and don't really have any plans to take the Tunze offline. It does its job fine. To me I think what I would consider is, how much do you like to tinker? If tinkering and DIY is your thing, go with the float switches and make your own breakout box for the Apex and have fun. If tinkering is not your thing then price out each option and go with whatever looks better to you.
One thought, the Tunze osmolator outputs 12vdc to run a 12vdc pump. These pumps aren't 100% bulletproof. But on the flipside, they're cheap ($25ish if I recall). So if the pump fails then you can replace it for cheap but you can only replace it with another 12vdc pump.
If you would prefer to use a powerhead then you need a relay. You can either buy the Tunze relay (they do sell a version, around $75ish I think) or DIY something (I went to an electrical/electronic supplier and bought some relays, you have to mount it yourself in some fashion but you'll probably be able to do something in the $10 ballpark). So again comes down to your love of tinkering (or not
)
But if you want to go powerhead from the get-go then maybe float switches and the Apex from the start might be the way to go. So long as you're OK with playing around a bit to get it all done.
(For now I just stay with my DIY relay option and don't have to use up a controlled plug on my Apex powerbar. The Tunze is fine enough.)