What ohm load is best?

well no not necessarily. There are many amps on the market these days that will go down to one ohm but reach their max output at 2. In fact most JL Audio amps produce the same output from 4 down to 1 to allow for many different kind of subs and wiring configurations. Get the specific specs on your amp. Thats always the way to go.

The lowest impeadance rating is not always the best way to go if you want your amplifier to last for a long time. I have been repairing amplifiers for over 15 years and have seen many amplifiers that claim to be 1 or 2 ohm stable that are really only stable for a short time. They overheat very quickly. Most amplifiers are mounted in places that get very little ventilation, this is a major cause of them overheating. By connecting your amplifier in a 1 or 2 ohm configuration does not improve the quality of sound, it only increases the power output. Every time you lower the impeadance by half (from 4 ohms to 2 ohms) you double the amount of current being pulled thru the amplifier at whatever volume level you test it at. This may be nice for having a louder system, but it will wear out the components inside the amplifier faster. The only amplifiers I would trust to use at 1 or 2 ohms would be U.S. amps or Phoenix Gold.

my friend has an amp that is a 1 ohm load but the way he has it wired its getting an 0.5 load it sounds great but in time his amp will fry

If you want the best sound quality you would usually go with a higher ohm load, but if you are looking for loud, go with the lowest ohm load rating on the amp.

the lower the ohm the harder the amp has to work..

The lower impediance generally gives you a larger THD value... which means more distorion. Look at the specs on the amp.

To get the best from your amp, yeah, you want to use the lowest impedance rating that it can handle. you just have to be weary of the wiring and the power that you will be delivering to your speakers/subs at that level?