Argon filled is pretty much standard in commercial glazing. Argon will leak from polysuphide sealed units, but will stay in silicone sealed units.
FunkyMonkey – Argon typically drops the centre pane u-value of the unit by approx 0.5W/msqK which is a pretty big percentage drop.
As said above, a low E coating is required under building regs, but don’t go for Pilkington K whatever anyone tells you. It’s not as good as other coatings performance wise, and has a brown tint/colour to it.
Don’t pay more than £5/sqm for argon filling. Warm edge spacers will make little to no noticeable difference, so aren’t really worth the extra, especially in a uPVC window.
I can’t think of a single pro for a hard coating on the glass over a soft coating. Soft coats perform better, but are typically more expensive. Hard coats are old technology.
There are a LOT of different coatings you could get depending on what you want from your windows (looks, perfomance etc), but i’d just get a decent low e coated unit with a 16mm cavity (optimum for lowest heat loss with argon gas filling).
A laminate glass will help add an element of security to the glass, but if a crim knows what he’s doing, will still get through.