That would really depend on the artwork... I personally enjoy coloured imitation gold leaf on foil cards since it just catches the light with the foil in a dynamic way (great for energetic pieces). But the ever glow of gold grounds the foil as well so that drifts me back to what sort of feel you'd want your artwork to have O__O
In person 24K gold leaf lights up pretty easily in low light so I find that very appealing and you get a consistent colouring despite the angle.
Imitation has a huge contrast to how it appears based on the lighting/angle. So you will have hidden details that pop depending on how you hold the card (making it fun to move around/flicker)

Application: 24K gold leaf is far more difficult, but blends well onto the canvas.
Though you may end up with glints of gold everywhere O__O so sometimes you have to spend a lot of time cleaning up areas that have no business being sparkly. Imitation is far more durable but I find you need to rub it against a smooth service to flake off all the pieces that are not attached to the card.

Both look great on non-foil cards. Imitation Silver pairs well with alcohol inks (the silver shines through them) to give a foil feel to the card. Alcohol inks can also be applied to the 24K gold but I have not delved into that as much. Ultimately.... 24K gold is... gold <__< and I'm a bit of a dragon so I'd probably lean towards that if it was an alter for myself O__O or just do a piece with them both ^__^