which is better for a beginner a nitro rc buggy or an electric rc buggy?

Start electric for sure. Nitro adds a whole level of complexity to the hobby that can be frustrating when you are just starting out.
References :
http://store.smallhelis.com/

dan is right but elec. is more money up front but in the long run is cheaper. i started nitro and i wanted to pull my hair out allot but it was a great experience to learn and u can allways find help and tips online. i run elec. now and it is fun for the fact that it is fast and quiet and can be run in the house a bit but when your battery is dieing your out of luck till u charge it again witch can take an hour on a good charger. i would go with the elec. buggy if u have the funds but if not go for nitro, it is cool in the scents that it is a motor and makes noise like a real buggy or truck does.

here is a great elec. 1/10 scale 2WD buggy rtr
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXYYE2**&P=0

here is one of the best rtr 4WD 1/8 scale buggys on the market
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXYED3**&P=0

keep in mind that u will need a battery and charger, for a good battery u will be spending around $80 and the charger is around the same price.
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here is a good nitro 1/8 scale 4WD buggy for a great price
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXRUS1&P=0

u will have to buy fuel(1 quart=$11)
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMGE5&P=7

a glow ignitor
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJGS6&P=7

and thats just what u need to start the buggy.
References :
9 years of rc racing