Bear in mind, you only had 750 in the regular saver account in the first month, 1500 in the second, etc.
You're only getting interest on what you have lodged each month.
With a lump sum account you're putting 9000 away up front.
So you can't compare the two directly.
The best return is simply indicated by the interest rate.
If you want to maximise your return on a lump sum, put it into a lump sum account like NR, then drip-feed it to the regular saver each month.
Note - you need to watch the interest rate on regular savers - e.g. Halifax have recently dropped their rates on accounts taken out before a date in Oct 2006 - so your account may no longer be competitive