WampServer is known as the easiest to configure. Your question is subjective, so I refrained from calling it the best. Different servers are suitable for different purposes. As far as I know, the BEST server is still working, some of its functions are:
<kidding>
- Reading the mind.
- Debugs itself and places scripts.
- Absolutely no downtime.
- Auto-tuning for every module ever known to mankind.
- It can only be hacked.
- It runs on 1MG of RAM and requires installation at 600K.
</kidding>