the kernel you choose depends on the system you have
if you have more than 4 gbs of ram, the pae or pae.bfs are good options because those kernels will handle over 3 gbs of ram so any ram over that 3 gb limit will not be wasted
if you have a amd 64 bit capable cpu the a64 is good option, some other intel cpus can use it well(atom for example)
the bfs seems to be good for everyone and the one without extra modifications is the one used default if i remember correctly, special for servers seems to be the description
you can install 2 or 3 to test them, i had 5 installed without problems
the first time you install a new kernel and select it on the boot menu it will have to check for hardware and also add driver modules, this can take time, 3 or 4 minutes so be patient
each new kernel you boot will repeat this procedure
don't remove the old kernel, leave it just in case that no new kernel helps you or refuses to boot
