Best lightning?

I have a 3x3x6 tent and want to optimize the space with the best amount of lighting as possible. I want to use LED's to keep energy and heat down.

What type of wattage would be suitable for that space?

Thanks!

320 watts worth of high quality led diodes, such as samsung 301b/301h based boards or strips on a 320 watt driver. You could run up to 400 watts but most phenotypes wont come close to needing that amount of light to flourish.

What type of a budget are you trying to invest with?

Well, my favorite has to be ball lightning...

If you're using top-tier diodes like a lm301b or h, to achieve a 750 average ppfd for that space will need about 330 watts.
System wattage is determined by driver rating-they are usually available in 240, 320, 480, and 600-watt output ratings.
I'd either look for a system using a 320-watt driver or if you think that you may want a larger space, use a 480 or 600-watt fixture that has dimming capabilities.