First of all, what kind of setup do you have? You asked about a nine cog cassette so is it nine speed?

I would suggest that you go with a regular 11-32 or 12-36 cassette for nine speed. The gaps are close enough that you're not constantly shifting the front to find the in-between gear ratios.

The whole point of the Megarange cassette was to have closer gaps on the smaller cogs. With 8 speed a regular wide range cassette isn't that bad (you still shift up front more) but with a 7 or 6 speed you'd end up with gaps big enough to drive a truck through. The Megarange cassettes just aren't necessary with 9+ cogs.

Keep in mind that if you're probably going to need a long cage derailleur when going to a wider range cassette, if you don't have one already.