I'll start by saying that I don't thinks its really a good idea to choose what you eat on the basis of any single nutrient, however beneficial it may be. Food like beef or lamb are complex containing many different nutrients in varying amounts, the best plan is usually to eat a wide a varitey of foods.

To answer you question. Grass-fed lamb on average probably has more conjugated linleic acid (CLA) in it than grass-fed beef, but not a great deal more. However this depends on several different factors:

• What the animals are fed: Grain-fed cows or sheep will have less CLA than grass-fed. Lambs supplemented with seed oil (such as sunflower oil) will also have higher CLA.
• Lambs born as twins have less CLA than single lambs, they have to share the milk containing the CLA. Lambs born to mothers with high CLA levels will get more of it in the milk.
• Individual genetics: Two different lambs fed the same diet can have quite different percentages of CLA in their meat.
• The CLA content of meat and fat varies in different parts of the animal.

So as you can see any number given for the amount of CLA in different meats will be a very rough estimate of the average amount. Both beef and lamb are a good source on CLA and many different animals contain smaller amounts.