Sammy,

The bigger optics the more light the telescope can gather,some say bigger is always better and though true to the discription it is not really true.
Truth is we all would love to have the biggest possible telescope we can afford but unless you have a permanent place to mount it the size of the telescope will determine how much you use it believe it or not.
A 24" telescope would be great,(we all want one) but take into account what is required to move it to viewing location, setup, collimate, cool down and such and you begin to see the problems that can be involved with larger scopes.

Three things you should consider before purchasing are of course price, portability and ease of use,a telescope you can setup easily and start using in a few minutes will get more use then one that requires more work and time.
Check this link out, it should help you decide...

http://members.aol.com/KDaly10475/telescopebasics.html

BTW.. those department store telescopes are not all they are cracked up to be, purchase from a telescope dealer if you can.

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Rick M
http://groups.yahoo.com/group/AllAstronomyAllTheTime/

my astronomy & a.t.m. site
http://www.geocities.com/optical_stargazer