iPhone To JB or not to JB? That is the question.

I have an old-ish iPhone 4 which was doing the job fine until I succumbed & let Apple's last bit of interference (iOS 7.12) ruin it. It was fine on 6. whatever but I wanted to install a new app which required the 7.12 update. I now hate the phone. It's slow & cumbersome, some of the fonts are unreadable and a couple of useful features have been disabled. It's actually costing me money in lost calls (I have to call back) and unintentional calls (voice-activated calling can no longer be disabled so it phones people from my pocket!) so I am now at point where I want to break free from shackles of Apple Corp: Do I just replace it with an Android phone that does what I want it to do or do I JB the thing? Presumably JB would give me more control over it again (I'm asking because I've never really looked into it before) would I have the luxury of being able to revert to an older iOS or does it simply open it up to more app's?

I had an Apple Iphone 3GS which was a cast off from my daughter. I decided to jailbreak it so that I could install a hacked TomTom on the phone. Its been a long time since I jailbroke mine once it is jailbroken I think you can chose which IOS you load on the phone. I do not think I can post a link but I found a site called Sinfuliphone to be very useful when it came to jailbreaking the phone.

Many thanks for the helpful advice. I will have a look. I did actually treat(?) myself to a S5 mini at Xmas and I have to say it is rather nice to be free of the shackles of Apple Inc.. Don't get me wrong, the S5 has its issues, apart from everything else, Google (via Android) can be very invasive but I'm gradually getting it around to my way of thinking. I think!
But I will certainly have a look at that site, it sounds interesting if nothing else