The McVities Jaffa Cakes are pictured here because that's what we ate, and are the more famous of them by far. But frankly everyone's in on the act.
Nevertheless, if you Google "jaffa cakes" (which I did), you'll find (as did I) that McVities have sort of cornered the market in publicity, at least. Relentlessly springing in-jokes on the population (like Tango and Marmite before them), they aimed to make buying McVities' Jaffa Cakes a sort of post-modern statement, and act of buying in to a grand joke.
When it comes down to it, though, I expect that the average consumer would, like I, just reach out and grab the first thing with "Jaffa Cake" on the box, not realising that there's any competition at all, let alone a hotly-contested war.
They've been discussed at great length across the internet, especially their indeterminate cake/biscuit status. Customs and Excise, hoping to wrench a few more pennies from the kind of people who tend to go for them (students and the financially circumscribed), defined them as biscuits (which attract VAT), the manufacturers as cakes (which don't). This much is endlessly repeated: it's a Dreaded Interesting Fact.
What I find interesting is that due to this ruling we now have a scientific and firm definition of the difference between cakes and biscuits viz cakes go hard and biscuits go soft, which wouldn't have happened were it not for the ruling, which is curious.
If it were possible to create a true cake-biscuit hybrid, therefore, we'd have something that remained relatively firm forever.
Anyway, the box usually carries at least one in-joke, all part of McVities' attempt to define themselves as The Only True Begetter of Jaffa Cakes. In this case it's a helpline number for "Jaffaholics Anonymous", though I don't know what they'd tell you other than a) Jaffa Cakes aren't actually physically addictive, though they are a bit more-ish, which isn't actually the same thing and b) you're next phone bill will be quite a bit higher than you're expecting, especially if you ring the number again.
They're also available in other flavours (the German version, which has none of the airs and graces of McVities' product, comes in two varieties - Orange and Raspberry. I prefer the Raspberry). A pedant would suggest that a Jaffa Cake without orangeness isn't a Jaffa Cake, as the Jaffa bit is a reference to the Oranges from which they're made. That pedant ought, perhaps, to be beaten gently but persistently with a full box of Jaffa Cakes (any flavour), even if they are right.
The box was in the flat for a total of fifteen seconds before it was folded flat and demoted to Merely Garbage Status. I almost feel bad for the box, but I enjoyed the cakes.
Or, if you work for Customs and Excise, biscuits.