What lens should I choice?

I have an Nikon D800. Even though It's a professional camera, I'm novice.
Besides, I have 3 lenses which are 24mm-70mm F/2.8, 70mm-200mm F/2.8 and 35mm F/1.4.

I enjoy large aperture since it could blur background. Although 35mm F/1,4 is professional which I learned from its terrible price, its blurred effect is not what I want.

So which lens should I choose?

ZEISS 50mm F/1.4?
SIGMA 50mm F/1,4?

PS: I felt reluctant if I spend a lot money but got something which I dislike.

Yeah, I feel your pain…

That's why I pop into my local camera store every now and again, just for a quick chat… And to get all the latest news that's happening in the world of photography…

Sometimes the sales staff will demonstrate the different kit before I buy it… That's all you need to help you make your mind up.

I'm actually struggling with working out how someone with a computer and access to the internet… Couldn't work that out for themselves.

I get the feeling that you'll be experiencing a lot of 'reluctance' with any kit that you buy?

Awffy Huffy hit the nail firmly on the head.
You need to go along to a camera store and try out a few lenses to get the right one.

Maybe you really need an 85mm f/1.2 - not sure if Nikon make one of those but Canon do.

This reeks of trollery. You have several thousand dollars worth of gear and are asking questions which a beginner could answer with a little research.

That, or you have far more money than sense.