It depends on your budget partly, but you can't really go wrong with an Alexander cage from Zooplus. I also think the Savic Hamster Plaza is an excellent cage but it's a bit taller and could work out a bit expensive to set up with extra shelves.
As Velma says, the Alaska, Barney and Alexander are all good Syrian cages. I personally think the Hamster Heaven can be a bit on the low side for large Syrian toys, and most of the plastic contents need removing as they don't really work.
I've never heard of a Syrian being unhappy in an Alexander cage! I have the Barney but it was a toss between that and the Alexander, and the Alexander was out of stock at the time. The Alexander costs a bit more but comes with plenty of houses and shelves and you just need a wheel. Whereas I bought an extra shelf or two for the Barney so it probably ended up costing the same.
Hamster Cages | great selection at zooplus