Your taste will influence choice but there are some things to consider.
There is a certain style associated with a wetroom floor, the uninterrupted floor expanse can enhance the perceived size of the room and creates a beautiful aesthetic by avoiding the colour and texture change of a showertray. The general feel and ambience is clean and modern, with no step up into the shower area, but there are reasonable arguments for either style.
Cost.
Have no doubt, a wet floor system will cost you considerably more than a showertray! All told, in a typically sized modern bathroom, the difference in cost could be in excess of £1000 GBP, and possibly more in a larger bathroom.
Additional cost comes with the materials and also with the labour for installation. The waste system is different and the drainage requirements are more critical on a wet floor. Naturally water needs to drain away downhill, so with the entry point to the drain being lower than with a tray this requirement can provide a challange.
Drainage.
Ensuring that the shower water can drain quickly is essential on a wet floor, to prevent water pooling in the shower area and even beyond. With a shower tray there is a defined lip which retains water in the tray area and prevents spilling onto the rest of the floor, but modern trays are shallow, so drainage still needs to be efficient. A blocked drain can cause the water level to rise above the rim of the showertray. Waste fittings for showertrays tend to be 90mm diameter now, rather than the older 60mm standard, allowing water to drain away quickly. Most wastes will permit a flow rate of around 25 litres per minute, which is enough for most shower fittings, a large rain-fall head typically delivering maybe 20 lpm. However it is essential to regularly clean the waste fitting to maintain this flow.
A wet floor drain in a central position will give a similar flow rate, but a linear (slot) style drain can provide more flow, usually around 30 lpm. The drainage speed on a wet floor will also vary according to the fall (gradient) of the floor area and of course the trap needs to be kept clean. Should some water spill beyond the shower area, the tanking (waterproofing) of the whole room floor will prevent leaks.
Many modern style showertrays, and particularly the slate effect type, are very slim and have almost no rim at all and so perform in a very similar way to a wet floor.
Enclosures.
A full glass enclosure of door and side panel(s) can be fitted onto a wet floor or a tray, and a splash panel arrangement can also be used in either situation, to provide a walk-in shower with an open access rather than a door.
The most efficient splash reduction is of course with the full enclosure, but again this is not really a big deal on a wet floor where the whole floor is tanked and waterproof.
An walk in style arrangement will always produce some overspray, and if fitted on a showertray the floor will get wet, but usually no worse than when you step out of the shower and drip on the floor! Common sense and a wipe with a towel will prevent any leaks. Again with a wet floor this is not going to cause a problem.
Sometimes a wet room is designed with no splash panel at all, and while the floor will remain watertight, consideration needs to be given to your toilet seat and toilet paper which will ideally want to remain dry, and also to any furniture fitted in the bathroom. Most bathroom furniture is constructed from melamine faced chipboard or other particle board. If this type of material is constantly being splashed with water there is a possibility of the board expanding, or "blowing" causing unsightly and basically impossible to repair damage. So advice would be to avoid a completely open shower area, unless it is a really big room and splashing will not cause you any issues.
