Which iPhone is better? Opinions please?

Ok I'm looking into getting a iPhone 4s. On the Apple website, the iPhone 4s 8GB is free (obviously just the actual phone, not the data plan.) but on craigslist, there's the same iPhone only 64 GB for $100. I need to know what is better. I love music and have a lot of songs on my current iPod. I have 105 songs on my iPod 4 and it is 32 GB. If I get the 8 GB, and put 105 songs on it, plus apps (such as social media: Facebook, Instagram, games e.t.c) will it run slow and the battery get worn out easily? Which is the better option?

NONONONONONONONON seriously never get the free iphone I always get the 200 dollar one which is the best but you can also get the 99 dollar one which is still pretty good you will regret getting the free one because 1 it only has 8gb which is seriously nothing 2 after about a year it will lag so much you will want a new phone right away 3 it only has 3G 4 next year it will be discontinued and you will have a slow old discontinued phone I would either recommend the 5s or the 5c if you can't afford that much right now defiantly go with the 5c because it works amazing not as good as the 5s but still good honestly there's no way to go wrong with iPhones if you want you can still egg the 4s because it's still a good phone but I would recommend a better one hope this helps