Ubiquinol is the reduced form of CoQ10 and they have done studies on the efficacy of taking CoQ10 vs. Ubiquinol, and due to age related declines our bodies start being unable to break the CoQ10 (Ubiquinone)down into Ubiquinal around the age of 40.
Ubiquinol and CoQ10 are roughly the same in price. With Ubiquinol I take 400 mg daily. I split mine up in the am and pm, although I have read in someone's post somewhere on this blog that they heard it is best to take it all in the am. It is fat soluble, so it is unlike Vitamin C where it declines over the day due to not being fat soluble, but I like to spread all of my Vitamins out to 2x's day for the ones that require 2 capsule or more dosages to keep levels more even.
If you go with CoQ10 make sure you buy it from some place like Puritan's Pride (they have a lot of discounts and sales offers online and you may not even have to pay tax. Shipping is often free if you spend up to $50 or $75/order, so order several if that is the case to save on shipping costs). If not, you can look thru the list via the hyperlink below for other manufacturer's or sellers of the Kaneka made Ubiquinone or Ubiquinol.
You mainly want to be sure you are getting a high quality CoQ10. I would do the same if taking Ubiquinol.
Here is a list of the companies selling CoQ10 or Ubiqinol made by Kaneka who own the patent on CoQ10.
You can also visit their site to find out why you have to watch out for other CoQ10 manufacturers, since some of their CoQ10 is even manufactured from tobacco....
Also, I take my Ubiqinol with 1000mg 2x/day Vitamin C; 800 IU 2x/day of Vitamin E and 300 mg of Alpha Lipoic Acid, because these help with the absorbtion and better performance of Ubiquinone or Ubiquinol.
I will add that diet, excercise and stress reduction are also very important beyond supplements.