Android: AsyncTask OR normal Java threads with ExecutorService

My application uses a Service to do some background stuff. I am using additional threads in the service to do some computation. For this purpose I create two threads every 5 to 10 seconds, which are running 5 to 10 seconds. But I don't know which thread-model I should use:

1. AsyncTask:

   Pros:

   • easy to use
   • android specific
   • easy UI-interaction

   Cons:

   • Since I have to use API level 10, there is no ExecutorService with fixed thread pool to execute the AsyncTasks

2. Normal Java Threads:

   Pros:

   • ExecutorService with fixed thread pool

   Cons:

   • Not so easy to handle, e.g. UI-interaction

Which model is better to use? Especially in concern of performance. Is there a heavy overhead when i am using AsyncTasks, and is the ExecutorService faster in reusing the threads than Android in creating new AsyncTasks?