Is is a warehouse/indoor or outdoor application?

Stand-up trucks are usually used during the indoor operation, in warhouses, where the surfaces are smooth, and the space utilisation is meaningfull.

Rider electric trucks (excluding reach-trucks) are mostly intended for indoor application, but out of rackings, IC rider trucks are for outdoor work, where surfaces are sometimes rough and the distances are longer.
I think, the decision should be made basing upon application.
The stand-on counterbalanced trucks are pretty rare in Europe and are being used only in very tight areas.

If the choice is like: warehouse, high stacking + sit-on reach truck or stand-on stacker, I'ld take the reach truck (if the aisle width allows). it's definitely more comfortable and safe.

Stand up vs sit down should be determined by the intended useage. Each has an advantage in their own way.
The stand up would have a tighter turning radius & easier operator mount/dismount.
The sit down has the availability of higher capacities & has a lower center of gravity-therefore is better suited for ramps, inclines, etc.
As far as batteries, both types should be able to operate thru an 8 hr shift without a recharge.

1. Stand-up counter balanced electric tend to be max lift capacity limited - commonly less tthan 5K basic lift capacity. A few manufactuers offer a 5K capacity but the unit get to be very long.
2. A 3 wheel (most actually 4 wheel w/ tandem steering tires in lieu of a single steer) is a nice alternative to a stand-up or 4 wheel counterbalance as most operators can step to the ground from a seated position which makes it suitable for frequent on/off operations & gives the operator soem in teh seat time while traveling. Again capacity is limited - most are 4K lift capacity - there is one company that has a 5K but the ground to seat height is higher than most due to the height of the battery compartment.
3. If you decide to go to a stand-up or 3 wheel make certain you get a battery w/the largest kWh rating - this will give you more run time between battery charges. The battery compartments are smaller than a 4 wheel electric - which simply means they can hold a larger kWh rated battery.
Some folks will talk about battery size in terms of amp/hr size - all this means is the rated discharge rate over a 6 hr (some brands for Europe or Asian countries will use a 5 hr rating.) In my simple mind - amps (resistance to flow) equals heat and amp hr ratings have little to do with run time and kWh is equal to power (energy) has every thing to do with run time on a single battery charge.
I am from a simple sales & marketing back ground and like to reduce all that technical jargon down to an understandable level and if you want to know all that stuff I'm certain someone can explain it all but get a big cup of coffe or two and a nice easy chair with a remote handy for the flat panel TV.

So I get out of hot water with all these "service engineers" - I will say when it comes to properly repairing and/or trouble shooting or suggesting option to resolve operational issues you need to understand the details of that stuff.
Just my 2.5 cents worth.

I would offer a big concern in making this choice is how often the operator has to get out of the operator's position as part of the operation. If the operator stays in the seat for hours at a time then a sit down, but if the operator has to get out of place for each pallet movement, then a counterbalanced stand up end control may make more sense.