I have and use both, depending on dive site and conditions. Either model fin is sturdy, though the Apollo's strap post can break outof the rubber. Either fin is better with spring straps, I highly recommend you spring for them.
The Jets work with any kick, though best with the frog kick, for me anyway.
The Splits can do various kicks, but only really work well with a modified flutter.
The Jet Fin has better control, can generate more power, but will be a lot harder on your muscles. The Split Fin is easy to kick, but you can run into problems in a strong current, when moving a lot of gear, or both. The latter happened three weekends ago. I was diving with a couple of other rebreather divers who used the Atomic split fins (by all means pretty good splits) as we ran into quite a current at the end of the dive. They were clawing their way back to the anchor line along the bottom while a swam right past them. Much to be said about streamlining and good fins, though the swim was physically taxing.
Last but not least there's the price, the Splits cost around $180, and well over $200 with spring straps. The Jets you can get for around $75, so even with spring straps they cost less than the Splits.
If I had to choose either the Jets would get my vote hands down.
In the end it's a personal preference, if you have a chance try both before you buy.