Ok well while everyone's answers are true I don't think they answer abyssis
Ignoring the fact that you don't get the use of a full core, let's focus on the two CPUs.
Now for your purposes (LEMP stack is it?), either cores would be more than sufficient for any task.
For this "breakdown", I'm going to assume E5s are 2.0 GHz cores while E3s are 3.3 GHz cores (most common cores from each "group").
E3s usually provide higher GHz, definitely helpful for unoptimized software which haven't been designed to run on multiple cores. The unoptimized software would have a max GHz "capacity" of 3.3 GHz in comparison to 2.0 GHz. Most software (even gameservers) usually are optimized for multi-core performance, (used to be an issue in minecraft though but I think they took care of that (anyone want to correct me?)) so I don't see that being a major issue unless you're running old code. But comparing single cores (one against the other), E3s win due to single core capacity.
If I recall, E3s have a limit to around 32GB RAM, while E5s can have (if I recall, I am a bit intoxicated at the moment) up to 768GB of RAM (although most of them I see are around 128 GB or 256 GB). This also means E3s have less density (clients per server, unless you're buying from YOU KNOW WHAT provider in which case then your SOL), but on the flip side the nodes are more fragile (in terms of your next door neighbors), therefore it's easier for the node to be affected by a single user. E5 nodes usually have higher server capacity, which of course means higher density, but also means the servers can take more "hits" before your next door neighbor's operation affects your own performance. It's a two way street here, but I'm going to give this one to the E5.
Provider side, E5s are much more economical, easier to maintain, and provides higher levels of profit allowing them to invest more in growing the company. For clients, this generally means the provider has a less change of suddenly disappearing in the night (less cost for colocation, less energy costs, etc. but of course higher initial costs but if they already bought it then this is usually isn't that big of an issue).
Of course this is all very general talking and depends on numerous factors (provider's business plan, profit margins, server administering habits, etc.), but in terms of RamNode you can't go wrong with either or. For your uses I'd suggest E5s specifically (in my opinion, less percent chance for noisy neighbors to be a problem). Nick runs one solid operation so you can't go wrong
haha damn you concerto49
! Beat me to it!
I work for Catalyst, and majority of our nodes are Dual E5s for this exact reason.