Supplementation method is a very personal choice and it's hard to suggest a single "best" method, much less even generalize, without being at least a little inaccurate. I'd suggest reading up - if you go in the Chemistry forum, I think there's a sticky there with links to online articles about the different methods, which will help you understand the differences.
Kalk can handle a tank stuffed with SPS, the only real limiting factor is evaporation. Some people find they're not evaporating enough to give them enough of a kalk dose, since you typically don't want to dose more kalk solution than the volume you're losing through evaporation.
2-part gives you higher resolution of control (i.e. you can adjust Ca and alkalinity separately, as opposed to Ca reactors and kalk where you can't). It's not linked to evaporation. A potential drawback is that you either have to manually dose the solutions each day, or buy dosing pumps.
With kalk or 2-part, you've essentially got direct control - you're literally dosing the stuff you want in your tank.
A Ca reactor is essentially indirect control - you control flow rate and CO2 feed rate to a reactor that "generates" the stuff you're trying to dose (Ca, alkalinity, trace elements). Hence to some people there's an added level of complexity, because you have to understand how adjustments to flow rate and CO2 dosing rate translate into changes in the tank. Ca reactors are also arguably the most expensive (up front). "lifetime" costs are hard to compare between the three because there can be huge variability in raw material costs and dosing rates.
I'm typically a big fan of dosing kalk - you've gotta dose topoff water to replace evaporation anyways, and it's simple to configure an ATO to dose kalk instead of plain water, killing two birds with one stone. Of course, you need to design the system carefully so it can't nuke the tank.
On my current tank build, I'm switching to 2-part, because I don't anticipate a typical evaporation rate, so I'm anticipating that kalk wouldn't keep up with demand.
