Disclaimer: I don't have either of them, nor I have hands-on experience. So, all these are only hand-waiving.
E3631A looks to me like a dinosaur: it has a single display showing only one channel and only two parameters (compare that to rigol). It also doesn't seem to be a reliable unit, I've seen quite a few repair videos, and broken units on ebay. Some traces on pcb are too thin and can develop a crack (like the one that drives power mosfet gate). It's also believed to be over-engineered for what it does. VFD display is often dim on units I saw on ebay, and brightness often non-uniform. Current is also only 1A on two main channels, and channels are not isolated. It doesn't have a usb or an ethernet ports.
So, I'd sell E3631A.