Depends whether you buy the phone direct/outright or subsidised by a carrier (which I believe is now, finally, an option in Belgium).
If you buy direct, I wouldn't worry: the OTA update to 4.4 will come through and (in my experience with a Nexus 4) it's a fairly painless upgrade (so long as you're patient and don't do anything daft while it's happening). If you buy direct: go for it.
If you buy through a network, then you need to find out how good the network is at pushing through Android updates, particularly for low-end (price-wise - the G is a superb phone by all accounts) phones. I have to say that most networks are not very poor at getting updates out and when I lived in Belgium about a decade ago, the Belgian networks were particularly bad at just about everything, so if you do buy subsidised and you really want 4.4, might be best to wait.
The G is remarkably low priced: if you can afford to buy it outright, it's definitely the way to go.
Re 4.3 v 4.4: the upgrade has a few neat little touches that are very nice and it definitely makes some things quite a bit prettier, however 4.3 was perfectly good.