Hey fellas I need some advice.

I'm building a PC for Houdini and I'm considering getting the RTX 3090 24GB for it, but my friend is advocating for me to get the RTX 4070 Ti Super 16GB instead. I'm aware 12GB VRAM is the minimum requirement for Houdini to operate but I also searched that more vram is needed for more complex scenes and whatnot, which I do want to pursue (Pixar level quality stuff).

Any opinions on this? I can't get a straightforward answer anywhere.

There really isn't a straightforward answer - it simply depends. More Vram is always better, the question is how much you're willing to spend. I've attached a screenshot from a recent pixar talk. It shows how much Ram they needed for each of their movies. The bar size in each category is the percentage of shots that fit into a specific memory bracket. The point they made was that they can now render most of their scenes on GPUs... not consumer ones though.
Do you need that much vram for your projects? If you don't know, then probably not, and if you do.. you already know how much you need.

The best resource I know to compare GPUs for 3D rendering is the Blender Open Data page, it shows rendering times per GPU using Cycles (Optix), the RTX 4070 TI Super, which is the GPU that I have, scores 7082.68, the RTX 3090 scores 5326.65, the higher, the better...

Blender Open Data [opendata.blender.org]

So far I am quite pleased with my GPU and 16GB seems enough to render most scenes with Karma XPU !!!