Original Nautilus, either the 5ml, which you can get quite cheaply on Ebay from Chinese vendors...mine cost me £6...and it is a genuine Nautilus, not a knock off! Or the TPD mini version, which is just as good, but only 2ml. Get the stainless steel cage Aspire makes for either version, that has a built in glass tube in it...and it's virtually indestructable & looks cool as heck! Takes the same BVC coils as the N2 or N2S.
The N2 is perfectly good too, as is that Zenith, which i also have...but there's no MTL tank that quite hits the mark like the original Nautilus does.....perhaps the greatest MTL tank ever made, in my opinion.
I cannot comment on the Zlide...never seen one!