I like the Nestor Marten. I haven't seen it in person but I think that if someone offered to trade me one for my Vigilant I would take them up on the deal.
The VC and NM look like two very comparable stoves. The Nestor marten has the advantage of a side load door for wood in addition to the top load and front door,
You can also order the Nestor Martin with a back boiler, which is a nice feature.
The VC has the ability to have the flue exit out the top or rear by reversing the flue piece, if that is a benefit to you.
I also like the way the VC routs the exhaust gasses from the top of the sides to the bottom, around to the back, then up and out the flue. A long exhaust path to extract as much heat as possible. You can also open the damper and rout the exhaust straight up the flue.
It is also rated to be able to burn bituminous coal.
The swing out ash pan is also a nice feature on the VC.
The shaker grates on the VC are not very aggressive, and the ash needs to be raked with a poker tool from below the grates in addition to shaking to effectively remove the ash, which is not a big deal, although it is I think the stoves weakest link.
I don't know the exhaust path of the Nestor marten, but it has a good efficiency rating of 80.5%
The only thing I cant find on the Nestor martin is the shaker grate configuration which I would have to know before deciding to buy. Does it shake? Does it cover the entire bottom? If not don't buy!!!
I don't think you could go wrong with either stove. They are two of the nicest looking coal stoves on the market.