Hello and welcome
If you can afford it I would go for the Alexander or Barney cage
The Hamster Heaven is a great cage but some Syrians can outgrow it and most of the plastic contents end up breaking or being taken out because they get in the way of a wheel or a house - plus the tubes are a bit small for Syrians really - some hamsters can get stuck in them. Definitely not Rotostak. Been there, got the t-shirt.
The Alaska, Barney, Alexander and Hamster Heaven all have a good deep tray for lots of substrate, which is something hamsters need. If it's deep enough they can even dig tunnels and burrows and other normal hamstery behaviour things.
The Barney is a bit cheaper than the Alexander and about the same size, if the cost is too much for the Alexander. On the other hand, the Alexander more or less comes set up and ready to go with almost a full extra level of shelves and 3 houses - you just need substrate, wheel, food, water and a few toys (tubes, hidey places, tunnels etc).
The Barney also comes with a good house and a good sized shelf, plus it has an 8" wheel - which would do temporarily for a starter wheel until you got something else. Although if you did get a cage from Zooplus it can be a good idea to get the 28cm Trixie wheel at the same time because then you don't pay postage on the wheel.
Trixie Small Pet Exercise Wheel | Free P&P on orders £29+ at zooplus!
This page shows the Barney, Alexander, Alaska and Hamster Heaven. Any of them are good for a Syrian really though. The Barney and Alexander both have narrow bar spacing of about 7mm - this is supposed to help prevent bar chewing - it's harder for them with the narrow spacing. Although the bar chewing is probably just because the current cage is too small, but also because your hammy isn't happy with other things about the cage too. They try and let us know if something isn't right for them! eg if a wheel isn't working or is too small, or if there isn't enough substrate, or they can't reach their food - they have to alert us somehow!
Hamster Cages | great selection at zooplus
If you did go for the Hamster Heaven I would remove the penthouse and tubes.
I had the Barney cage for our Syrian - upgraded him from something the size of the Hamster Heaven because it looked too full once I had a big wheel in there (he was a particularly large Syrian and needed a 12" wheel).
The might look a bit plain compared to the colourful ones with tubes, but they are good for Hamsters and you can make them look nice with toys etc. Tubes as floor toys are better than connecting plastic tubes which have bad ventilation and are also an escape route.