I like PerfectDisk - but I've never used DiskKeeper, so can't compare.
Regarding 'disk thrashing', PerfectDisk can be configured for manual-defrag only - and I suspect DiskKeeper can as well.
If not selectable by menu, you can identify the app's running processes and change the appropriate processes from automatic startup to manual startup. That's what I did with PerfectDisk. No problems.
If you're unsure about which process, the ProcessExplorer utility will identify vendor-processes by vendor name.
Hope this helps!