Slater's does water-slide GW transfers as does Fox.
Also Peco, for their ex Webster kits.
I'm skeptical about the shape of the large letter "G" - the curve should not be thinner top and boots than it is at the left-hand side. The smaller "G.W.R" for pre 1904 look good, as do the italics texts (though there is a lot of variation on the prototype, so you could have a range of styles of this and be equally right/wrong).
I would keep away from Pressfix/Methfix from HMRS - too thick and tend to curl and adhesive unreliable.
I've used both successfully, though I prefer Methfix for ease of adjustment before committing the transfer to a position. The HMRS sheet provides a very large range of specialist texts which is both a benefit and a disbenefit - you get things you can't get anywhere else, but you pay for things you'll never use. Beware of methfix on acrylic paints, which can be softened by the meths/water solution.
Small texts on the HMRS transfers can be a bit over-scale. This may apply to others but I haven't noticed it specifically. There is a perennial problem for Edwardian modellers (or perhaps modellers of the Edwardian period) that you sometimes need to fit a text into a narrow space, where on the prototype the painter simply squashed everything up. Typical cases are fitting 6 digit running numbers on the end of general merchandise wagons between the corner plate and stanchion (there's a reason I have wagons with running numbers 7460 and 41211...) and any text that has to fit the panels on an iron mink. I am about to have that issue with the Accursed Serpent, described elsewhere on the forum.
As a general comment, the shade of white varies between manufacturers, from a creamy white from the HMRS to a bluish white from Railtec, with points in between. Beware of mixing and matching from different ranges to meet your needs. It's possible if you are going to weather the wagon, but even then some care is needed.
Nick.