You will often find that the advice you get from your kitchen supplier will be biased based on the products that give them the opportunity to make the most profit. I work as an independent kitchen designer (therefor making my money on the design irrespective of the materials) and constantly find that joineries try to sway my clients away from what I have specified based on what makes them more money.

My advice would be that you will get better long term life out of polyurethane doors, but you will also pay thousands of dollars more for them, so you need to assess for yourself if it will be worth it.

Some points to consider; vacuum formed (vinyl wrapped) doors will last very well provided that they are a reputable brand and the design is considered. For quality , durability, cost effectiveness and flexibility of styles I would suggest Polytec. They back their product with an extensive warranty. A good kitchen designer will ensure that appropriate allowances are made to prevent heat issues effecting the vinyl doors. These include supplying & fitting a heat guard around any built-in appliances and adjusting the position of the wall cabinets. You willI have problems with the overhead cabinets if they are positioned too close to the stove AND if you don't use the rangehood. If you purchase a good quality rangehood & ensure that you use it when cooking on the stove the vinyl doors will be fine.
Also worth noting whilst the vinyl doesn't 'chip' as such it can still be damaged, with damage looking more like the marks / scuffing you get on leather surfaces (think of the toes of your shoes). It does take a fair amount of effort to cause this damage.

With the polyurethane doors you will be looking at several thousand dollars more expensive than a vacuum formed door. One of the greatest benefits is flexibility in design and colour (including the ability to have much sharper profiles). Yes it is a painted surface and any painted surface can be damaged by chipping, however the painted surface is still quite durable. The majority of damage I see is usually not from regular kitchen use, but rather from kids who have snuck in with their metal tipper truck and crashed it into the cupboards. The beauty of it is you can touch it up with some matching paint and you will probably never notice. You will also be able to remove a door if the paint is badly damaged and take it into a paint store for re-spraying (but please be aware the colour will not 100% match due to the aging process of the other doors).

Essentially there isn't really one right or wrong answer, it comes down to budget and the intended lifespan of the kitchen.

As far as natural granite versus stone (Caearstone, Quantum Quartz etc) I would say this depends more on the look that you are after.
If you actually like the look of natural granite & have a particular variety in mind you will not find a 'stone' product to give you that look, you are better to get the granite. The cost of granite varies astronomically depending on the variety, where it is mined from, how rare it is, etc. It will usually be more expensive than Caesar Stone. Natural granite can have fault lines in it, which is basically an area which has a propensity to crack. If it has a fault line it is likely to be discovered when the product is cut to size and the stone mason will have to get a replacement. Sometimes they like to scare you into thinking that your benchtop will just randomly crack one day but it is highly unlikely to have a fault line in the first place, and if it does, it won't crack unless additional undue stress is put on it (Like walking on the benchtop to change the lightbulbs!).
'Stone' which will be referring to manufactured quartz products like Caesar Stone, Quantum Quartz, Smart Stone, Silestone etc. is the most popular option for stone benchtops today. It is a man made product and is produced from quartz, resin and various aggregates and colouring agents. It is more cost effective than natural granite, but has a much more consistent look due to the fact that it is man made. Some people who like natural granite do not like the consistent pattern within the man made stone. Other than if you want that 'natural' look, it will be the better option for you as it is generally more cost effective and is also more stain resistant.

Marble is a big no-no for kitchens. It is expensive and highly impractical with propensity to stain excessively, and requires regular expensive sealing.

Thinner 20mm stone is the fashion starting to come through from Europe but it really hasn't caught on properly yet. I would go with what you prefer the look of, as this will change again before the lifespan of your benchtop is up.

Good Luck!