IPhone 4 or 2-years old iPhone 4s?

Well I've got a 2 and a half years old iPhone 4s and I really like it but I don't know if I should buy an iPhone 4 instead. Problem is the 4s is getting worse with age. Wi-fi got broken, fixed it, but it isn't the same again, wi-fi range got a lot shorter. Also, battery doesn't even last a day and I need to charge it again around 6 pm (I wake up at 7 am and charge it at night) and by the end of this year, this problem should be even worse. Finally, the signal antenna isn't working really great. But on the other hand, my brother just bought a new iPhone 4 and from what I've used it, I can say it feels much laggier than my old 4s. So which one should I get?

IPhone 5s