1.Giotto is the most popular - and quite sexy. a good alrounder.
2.VBM Domobar Jr is well made - heaps of steam which can be somewhat daunting.
3. Diadema is meant to have the best external finish, although I have never seen one. Good drip tray.
All very good machines. You have narrowed down very well *;)
Cant go wrong with any of them. Go and have a play and choose the one you feel most comfortable with.
There are slight price differences between them too, mainly due to capacity and boiler size. Some are bigger than others and the diadema comes in 2 boiler sizes. So looking at cheapest 2500 - most expensive 3000.
Hope this helps