Very happy with:
Deckadence flooring
Extra steps on back of trailer and built in ratchet tie downs. If you trailer every time these are definitely essential!
Docking lights
PNP (yes, that's an option, but shouldn't be)
Wedge/Surfgate (again, options that shouldn't be)
Folding windshield mirror mount. If you have do drop your tower to put your boat away in the garage, as I do, putting the tower arm on and off every time is a hassle. The folding mount is key in this situation. If your tower stays up then personal preference works here.
Lift up bolster driver's seat. May not be as much of an issue in a T23 but I can't see over the bow of my A20 when we're surfing if I'm not sitting on the lifted bolster.
Nice but not necessary:
Heater - Mine takes a long time to warm up and only stays warm when running, at idle it cools right off
Swivel racks - I like ours but if you're trying to save some pennies this is one place you can do so.
Colors/metalflake - again nice and makes your boat look cool but can be pricey
Deck-track - if I didn't have it I would go for gator step or sea-dek since the top edges can get slippery
The cooler - you can get one much cheaper on your own. I opted to NOT get the cooler but it showed up in the boat anyway.
Under-water stern lights - unless you are in the boat late at night regularly these aren't necessary
Extra bow cleats - there has only been one time since I got my boat in April that I wished I'd had them
As for sound I don't know what Axis is doing for 2017 but through 2016 I would def stick with SP1 and build on your own from there. They don't enclose the subwoofer in a box, it's just mounted to a plastic panel "free-air" and it sucks. If you don't want to build it yourself you can get a stereo shop to put in as good, or better, equipment for about what you'd pay for SP2. In my case the local dealer uses the same stereo shop for all their boats. The dealer orders the boats with SP1 and then has the stereo shop build "SP2" but with an enclosed sub and a pair of Rev8's instead of the 4 Icons (I that's what SP2 has). This is all still included in the price of the boat and gets financed as if it came from the factory. This way I didn't have to come up with the extra $2K+ in stereo equipment out of pocket. Plus it sounds way better than the factory SP2.
I'm probably forgetting some other things but those are the major ones I can think of.