I'm not an expert, so I'll just share my idea :)
Before you decide I think you should open your packs, then you should choose the best summoner who fits with your new cards.
I read a guide where an expert says that for a newbie are more important the monsters, and to rent the summoners to reach the silver league.
I think he considered the $/BCX: a rare monster is under 1 dollar, the cheapest summoner is over 3 dollars, if you like to own cards than renting them, I would tell you to buy monsters and rent summoners.
Personally, I don't like to rent, so probably that's what I will do...
Unless summoners become really cheap, in that case, I would probably go for the cheapest (probably the light summoner)
(sorry for the English, I'm Italian)