Unfortunately, you cannot go by what seems best on paper nor based upon what people recommend. The only way to know for sure which one is best for your specific system is to try both. The objective is to see both for yourself and decide which works best for you personally on your specific system.
In terms of stability, I would recommend you to go for kaspersky. Bitdefender may score good in av-test,but their products are too buggy, neither they do have good firewall nor it seems they have any intention to improve it. They have great sig. ,no one can deny that. but in real world, signature alone ain't enough. If you like bitdefender's sig. ,then go for emsisoft. Emsisoft has good bb also.
& regarding kaspersky, I personally use KIS ,with proper configuration it's a beast literally. You may not tame it all d time. It does some robust scanning if it finds something new & even if that something ain't new Kaspersky won't let it go easily. If you are looking for protection KIS is all good.
With 4 gb & i3 2120 & little bit patience , you will be pleased with Kaspersky.
If possible let us know your decision.
Your comp specs seems on the low side. and with 4GB of RAM plus mulltiple security softwares (not including internet browsing and other productivity task), I believe you will soon reach the limitation.