Agree that the Duna Multy or maxi duna multy would be ideal for a dwarf hamster, if you like that style of cage. The Duna Fun is far too small. Dwarf hamsters, although smaller than Syrians, are very active and need quite a bit of space. RSPCA recommend 70 x 40cm minimum for one dwarf hamster and 80 x 50cm for a syrian or two dwarf hamsters, but many people have 100cm cages for their hamsters as the minimum is just that really and it's surprising what you can do with the extra space to make it into a really good habitat. You could have different levels (eg a third of the cage sectioned off with deep substrate for digging, an end section of sand, an archway under the substrate to encourage digging and plenty of space for interesting toys and accessories. The buzz word is 'enrichment'. The more enrichment in the hamster's environment, the healthier it is for them.
The large version of the Duna fun would also be ok - it is the same width as the duna multy but with the extra barred section and the bar spacing is small enough for a dwarf.
http://www.portonaquapet.co.uk/-M271...ImJBoCP4vw_wcB
But for a few pounds more you could get this one - the maxi duna multy - the wider floor area is much better for a hamster than extra height and shelves/levels. It's a great cage and is suitable for both dwarf and syrian hamsters, so quite futureproof.
http://www.portonaquapet.co.uk/Cage_...a_Multy-M58956
Here are some examples of set ups in the maxi duna multy
I love this natural one! It's set up for a syrian but could easily be for a dwarf
Obi's natural set up is complete!
Maxi Duna Multy Has Arrived!
Scroll down for dwarf set ups
Let's see your cages (from January 2013)
The advantage of the tank style cages is they tend to be a bit lower and there is less of a risk of falls causing injuries. Narrow bar cages can be good too but they need setting up carefully to avoid falls.