After playing with my other fountain pens, I always end up coming back to my Lamys. I love how they fit my hand, how the Lego-like plastic barrels do not slide in my hand (unlike similar pens with metal barrels), and how user-friendly they are!
Other pens I love actually using are the Noodler's Creaper and Noodler's Konrad (my Konrad is shown in the photo laying next to the white gel pen), but I hate the ink-filling gizmo in the Noodler pens. The Lamy converter works easily and holds more ink. Sometimes I use an empty Lamy cartridge, refilling it with a syringe, for even more volume.
But what I really like about Lamys? I can leave them filled and unused for weeks and they still work when I pick them up again! My other pens need a bit more coddling and I don't always wish to take the time.
A downside to the over-use of my Lamys is that I actually wear the XF nibs down eventually. They then work fine as a F or even a M nib; I just prefer the finer line, so I sometimes need to replace the nib with a new one. The black-coated steel nibs seem to glide over paper better than the shiny ones.
I've also mixed up some of my inks to make new colors. Some advise against this but it's never caused me any problems. I've generally done this using only Noodler's and De Atramentis inks. I made this chart to remind me which pens are loaded with what ink --- the color differences don't show true in this photo, having been taken in low light.