This comparison is a bit of a surprise, usually I love Corgi Juniors, but comparing the Welly Porsche 964 Turbo with the Corgi Juniors Porsche Carrera, the Corgi model comes off poorly.
The two models are roughly the same size, around 1:60 scale, the Corgi is slightly higher but the length is the same.
I bought the Porsche Carrera on a recent trip to England, it cost me £4, the original model would have come with racing stickers, without them it looks under detailed, not even the doors are marked.
The Welly model by comparison is far more detailed, it has lights marked, black trim around the spoiler, door mirrors, windscreen wipers and a Porsche badge on the bonnet. I bought the model new from Carrefour for 6.90 lari (the same price as Hot Wheels and Matchbox here in Georgia, equivalent to £2.23).
The wheels of the Welly model look more realistic but the Corgi model would be faster on the track.
My choice: the Welly model, even though it is made in China and the Corgi model was made in Great Britain.