Talking about each company in general terms, as I have neither kit.
Warlord's resin vehicles are typically hand built. In cases that's led to some details being incorrect, or missing. Though they tend to have a decent level of detail in general (not as much as other companies like Die Waffenkammer however). In the past I've came across casting faults with them, like parts shrinkage (particularly with the track assemblies), bubbles, etc. Their customer service tends to be decent enough to deal with any of those issues. Shipping times aren't bad, as are the prices fairly middling.
Blitzkrieg 3D prints their masters. This has led in their case to some details being a bit large or simplified in my experience. I find their models have a very "flat" look as far as the surfaces go. Their barrels and other parts tend to be resin, whilst Warlord's may be either resin or metal - and include metal parts for other small pieces on occasion. Both companies vehicles lack detail on the underside of the models typically. As for shipping, Blitzkrieg take a bit longer - both in sending things out and the postal time (in total a couple of weeks to the UK - as opposed to a week or two at most with Warlord). Their prices are usually a bit lower than Warlord's, and they seem to have sales more often if you check their Facebook page (though on less items than Warlord's sales).
If you're deciding between the kits I'd probably recommend Warlord's, and then add any details they messed up. Blitzkrieg's models are a bit simpler, even if quality control in my experience is better - so there's less cleanup. If you want the models faster then buy with Warlord. If that's not an issue then hold out for a Rubicon release, as their's will likely be far superior to either company's current products.