The best part of jacoco it's that you can see how much methods are covered by test cases, what percentage of them get tested etc., also we could attach our metrics to generated report easily as well - for example if metric was "average time spent in each method" then this value would be included automatically inside coveraged reports too! It has very less user friendly UI (we used version 0.7), not so many plugins available out there but still good enought; I'd like to recommend using newer versions since they have lot more features than old one had.
We were solving problems with JIT compiler optimization before, now these issues no longer exist.