It's a question of personal preference really.
You get a much brighter sound with more attack if you use a plecky. But it's also useful to develop a basic fingerpicking style too.
There's no right answer but I'd say to begin with the plectrum while you're learning basic chords and how to put them together and then begin to experiment with picking.
Try to find simple songs that you like with 3 or 4 open chords in them (you will be amazed at how many songs you can get away with with G C A D Em !!) to practice on so it doesn't get too boring.
There's loads of sites on the net with the chords for popular songs if you just google say, oasis guitar tab or Travis guitar tab. Those sites are also a good place to begin to read simple guitar tabalature.
Good luck!