migrate to Electrum ca be done without any fee???
and second question, why not green address? is it a good choice too?
1. Yes, you're just effectively importing the private keys (for MBC) or the seed (for MBHD)... That effectively just replicates your MultiBit wallet, so you're not sending any transactions, so you don't need to pay any fees (Fees will only be required when you send the coins from Electrum)
2. No idea about Green Address... I've not used it.
The main reason for suggesting Electrum is that:
a. I know it works (personally tested it)
b. there are the n00b friendly video tutorials (that mean I don't have to explain how to do it!
)
c. In the case of MultiBit HD, Electrum is one of the few wallets that works with the Derivation Path m/0' (most wallets don't use this and/or don't allow you to specify it)