My first O gauge/scale engine was a Railking RS3 with Locosounds. To me it looked fine, but everyone said the Weaver RS3 is more prototypically correct.
So, I finally get a Weaver RS3, IMO opinion there's not a dollars worth of difference between the two as far as looks, both look the same as far as contours go.
The only big difference I see in the Railking model is the handrails are mounted underneath the walkway whereas the Weaver rails are mounted on the top of the walkway like the prototype. If that bothers you you can get a load of parts from P&D Hobby to make any of the RS3 models even better.
I replaced the molded-on fan exhaust screen on both models with a P&D brass see-thru screen and they look great. The Weaver model comes with plastic handrails, I replaced them with brass stanchions and rails from P&D.
If you're doing a specific RR, look at things like horns and their placement, how many they had, and which "phase" RS3 they owned. Louvered doors, exhaust stack type and placement, and minor other things changed over the phases.
I wanted to do an Interstate RS3, or maybe a couple of other RRs in VA, but in the end the only RR I could do without a lot of work (to the Weaver model) was the one I already had an RS3 for, Seaboard Air Line. So now I'll have 2 SAL RS3s!