Paleo: A general concept shared by multiple authors and gurus regarding the elimination of toxins by basing a diet on "Ancestral" foods. Core beliefs are "No gluten-containing grains, no legumes, no-lactose or casein (cheese/yogurt/milk), no sugar". There are many other various iterations (of which Primal can be considered one) that adjust these measures based on even more varied reasons. Classic "Paleo" as coined by early 2000's authors Audette (Book: Neanderthin) and Cordain (The Paleo Diet) would fall in the "Low Carb, dairy-free" camp, whereas more modern (Harris (Archevore), Jaminet (Perfect Health Diet)) proponents would allow for moderate-to-high starch intake, and slightly more leeway in regards to some dairy.
Primal: An adaptation of the Paleo diet as authored by Mark Sisson (Book: The Primal Blueprint) that focuses on carbohydrates and toxins. Primal allows for considerably more leeway in regards to dairy, some "safe" grain and other starches, and even fermented legumes. Diet can be adjusted to suit personal needs, although being completely grain, legume, and sugar free still seems to be the main objective.
Since all of these have considerable crossover, I would suggest looking into the specific authors. This thread should help you out...
The way I understand it, the biggest difference, is that Primal allows some full fat dairy. In my opinion, I feel that Paleo is more rigid than Primal, when it comes to food rules. I think tubers and night shades are thought of as acceptable on Primal as well. That's my take, from the information I've read. Hopefully that's helpful...
There's no statutory definition here. I use the umbrella term "ancestral eating" and I consider all the plans as variations under the same umbrella. Some recommend specific eating patterns and others engage in healthy dialogue about nutritional science: Archevore, Gnoll, Primal, Quilt, Cordain, Wolf, Jaminet, Kresser, CarbSane, Guyenet, etc.
They all have the same goal, they just differ slightly with regard to execution. The whole point is to maximize health, energy and longevity. Since humans aren't all the same, ALL the interpretations are correct for at least some of us.
Is one better for weightloss than the other? Or should I just experiment with it and see how my body responds?
Nobody knows. Everyone is far too busy redefining "paleo" and trying to think up excuses for why they need to add dairy and starches back into their diet. lol
I consider primal to be paleo + dairy, largely because the original founding fathers of paleo (Cordain, Wolf) were anti-dairy and Mark Sisson (Mr. Primal Blueprint) was more dairy friendly.
Re your question about weight loss, a number of folks (like Tim Ferriss of 4 Hour Body fame) suggest avoiding dairy if weight loss is your goal. But experimenting and seeing what works for you is absolutely spot on. If you can tolerate dairy (and especially if you can get dairy products from grass-fed cows), it's certainly well worth considering.
I don't have much dairy - some cream once or twice a week and butter cos I can't find coconut oil anywhere. Du think this is slowing down my weightloss? I don't tend to have fruit other than a little rhubarb a few times a week the rest is just veggies protein and fats. Should I cut out all dairy du think?
In addition to allowing dairy, my understand is that Primal aims to be a bit more flexible, aiming for 80% compliance, whereas Paleo aims for 100%. For example Mark Sisson wrote that if he's in a restaurant with a nice-looking bread basket, he might indulge, whereas Robb Wolf wouldn't. Is that at all accurate, anyone?