I know there are various strengths but i dont think its necessary to take 2 a day of 150mg. It clearly states that on the label itself. As far as experience i have taken Nexium, prilosec, prevacid and zantac. All of which were prescribed once a day.
Nexium is the best but if you are paying out of pocket then its expensive. But they came out with Nexium for which you dont need prescription, i dont know how effective it is though. My acid reflux used to be bad that i had to do upper endescopy and i never was prescribed any pills twice a day. Later on my doctor gave me Zantac 150 once a day.
Just my 2 cents.