I have a number of 51's, as they were my gateway drug into fountain pens.
As a first pen I would probably get an Aero, rather than a Vacu (Sorry @nemo). The Vac will be fine as long as it has been restored well (new diaphragm, mainly) but the Aero is bulletproof, and many can be found in the wild that need little more than a good flush out. If they do need servicing they are easier to work on, without any special tools, in my experience.
Colour, gold filled Vs Lustraly, nib width, that is all YMMV, and personal.
FWIW, my everyday pen is Aerometric, gold filled cap, fine nib, and I run it on my own ink mix, but also quite like Noodlers. Seems to work fairly well in them. That pen is one I built out of the parts of two broken pens I found in the same shop for cheap. Such is the fairly simple and robust nature of the 51 Aerometric.
As a first pen I would probably get an Aero, rather than a Vacu (Sorry @nemo). The Vac will be fine as long as it has been restored well (new diaphragm, mainly) but the Aero is bulletproof, and many can be found in the wild that need little more than a good flush out. If they do need servicing they are easier to work on, without any special tools, in my experience.
Colour, gold filled Vs Lustraly, nib width, that is all YMMV, and personal.
FWIW, my everyday pen is Aerometric, gold filled cap, fine nib, and I run it on my own ink mix, but also quite like Noodlers. Seems to work fairly well in them. That pen is one I built out of the parts of two broken pens I found in the same shop for cheap. Such is the fairly simple and robust nature of the 51 Aerometric.