Hi there, I can only answer the differences between the batteries as the rest is up to you. The Egg batteries are quicker and give you more time and are lighter in feel, Here are the stats. The green batteries run for an average of one hour, sometimes slightly more. ( Kat has one of the dinos you have so she can tell you the running time of the batteries and is a good person to give you feedback. I do know she runs egg batteries on her Pleos, only because she gets more "play time") the green batteries have to be charged for 4 hrs. Now for the Ucube Egg stats.
The charger shaped like an egg, takes the battery as well it has an extra port for charging things like IPODS etc, though to be honest, I have never used that extra port. The batteries are white instead of green and wiegh less so Pleo moves faster, no running or anything but everyone admits he seems to feel energized. The battery charging time is only 3 hrs as opposed to 4. The biggest differece is that you get 2 -2 1/2 hrs of playing time depending on conditions. I have never known someone to not like the egg battery. I run all my guys on them except the RB, but the RB batteries are pretty much the same thing as the Egg but for RB only.
It is great that you are getting two batteries, that I think is a good deal, Two of your green batteries are = to one of the Egg batteries. What I would do is run the green batteries and test them yourself, then if in the furture you can save up for a egg battery, you will have excellent backup, while your greens are recharging, you will have time to still play and interact with your new friend.

Also with any battery I sell here on the forums, I allways include a free Pleo item that everyone seems to like. I do hope you get your new freind this week and can start sharing in the Pleo love we all have.

RWM