The difference in caffeine concentration from latte to mocha is insignificant.
Based on the size, a latte's 16 oz will have about 108 mg of caffeine and a mocha's 12 oz will have about 106 mg of caffeine. If the sizes are different, then you'll need to convert accordingly.
In any case, Mocha contains much more caffeine, but it also contains much more sugar, which gives you a quick burst of energy only to soon feel sleepy and jittery. In contrast, a latte has less caffeine but much more milk, giving you steady energy over many hours without crashing or feeling jitters afterwards. With the levels of both being so similar in comparison with calorie intake, your best choice can simply be whichever one you prefer in taste! :)