I haven't had the opportunity to build the same vehicle from both companies, but I recently did a Rubicon Panzer III for a friend and a Warlord Panther A and SdKfz 251 D.
In direct contrast, I found the Warlord vehicles much more simplified, especially the Panther running gear was a disappointing combination of lack of detail and poor fit. The Rubicon Panzer III went together marvellously, with the most egregious issues being some clunky designs of parts that would probably have been too fiddly or not robust enough for the gaming purpose. The overall impression is excellent, though, especially with the much better designed running gear. The Rubicon one is far more refined than both the Warlord Panther's and Hanomag's.
In general, the whole affair convinced me to stay with 1/48 "scale" kits for WW2, purely for personal taste, mind, in how the larger 28mm figs look next to the vehicles and in that the detail is finer. A Tiger is borderline, and I do consider my Tamiya Tiger I to be borderline huge.
But for ease of assembly, detail and design, I would generally recommend the Rubicon models over most Warlord kits I've seen so far.