If you can run an ethernet cable to the Apex, then the WiFi of the new Apex is irrelevant. So that is one thing you need to consider. The other main thing to consider is if you think you will ever upgrade to a larger tank? The reason I ask is because the new Apex "may" benefit you more than the classic, on a larger tank. For example, the WAV units are far too much flow for you current tank, but they would be wonderful for a larger tank... like 75 gallon or larger. And the WAV pumps can plug directly into the new Apex, as opposed to needing to purchase a 1-Link module if you have the Apex Classic. Likewise, you probably are not using a dosing unit on your current tank because it's so small, but you may on a larger tank. That's where the DOS would come into play. Again, it can plug directly into the new Apex, but would require the 1-Link module to plug into the Classic. Same thing goes for the new COR15 return pump coming out... it can plug directly into the new Apex. I know that's a lot of what-ifs, but it's exactly what happened to me. I had a Fusion 30 with what is now called the Apex Classic. I then purchased my current Red Sea Reefer 450... which I have the WAV power heads, DOS etc. Now it didn't matter for me, because the new Apex didn't even exist yet... but it could matter for you.
So if you are not concerned about a possible future tank size upgrade utilizing the add-ons I noted, and you can run an ethernet cable to your Apex, then I would definitely just do one of the classic units.