The rule
Don't drive Cape Town to Kruger. It's eighteen-plus hours of interior that isn't your trip. Fly. Cape Town to the Kruger gateways (Nelspruit/Kruger Mpumalanga, Hoedspruit, or Skukuza) is two to three hours with one connection, and you arrive rested with a full day ahead.
The options from Cape Town
Fly to Kruger (via Joburg, or direct to Skukuza in season) for the classic self-drive or lodge safari. Aquila, two hours from Cape Town, is the easy day-trip — but it's a fenced reserve, not a wild one: fine for a taste, not the real thing. Sanbona, three hours into the Klein Karoo, is a better free-roaming Big Five option closer to the Cape, though it's a luxury-stay reserve, not a drop-in.
The honest take
If safari is a major reason you're in South Africa, fly to Kruger or the Eastern Cape and do it properly — two or three nights minimum. If it's a box to tick and you can't leave the Western Cape, Sanbona is the most honest option within a day's drive. Don't pretend Aquila is the safari; it's a wildlife park with a good lodge.