So far I have only used piston, and that has served me well and hasn't led to any problems, but again, I don't have experience with the other filling systems.
I haven't tried a variety of nibs thus far, I do like the fine nib on my TWSBI, but there's flex nibs. I'm open to trying anything. Flex nibs sound interesting.
The mini has done very well for me, I just want to explore with other pens.
Overall I'm not a huge fan of TWSBI's clear pen styling, but I love it as a writer.
I mean just to gauge my tastes, I find the Full metal falcon pilot to be really quite nice looking.
Got a chance to try the falcon out a few weeks back, and I kinda get what Binge was talking about. If you're looking for flex, I honestly wouldn't bother with the stock falcon; it 'flexes' but doesn't really feel quite right in use. As a soft nib however, its fairly nice, but I'd rather take a Pilot Custom 74/91 with a soft-fine in that case.
The Pilot FA nib (available with the custom heritage 742/743/912) is probably the best modern flex nib at the moment, but railroading due to the feed/ink flow issues is fairly common, and needs a good amount of patience, tweaking, and good flowing inks, to make it work well, and even then, it isn't as good as going vintage. I love my 912/FA, however.
The noodlers are okay if you do the mods mentioned well, but provide a crappy experience in their stock forms. Build quality leaves a lot to be desired imo.
On the topic of american pens, I actually really like the Franklin-Christophs. Great pens for the prices they're charging, and getting a Masuyama ground nib for an additional 15 bucks is a really good deal. Newton pens is doing some pretty awesome stuff as well, but the prices are a little out of my range for now.
Instead of the falcon, I'd recommend taking a look at either the Pilot Custom 74/91 with a soft-fine/soft medium fine; decently priced pens (if you buy direct from japan) which allows you to try out some flex (not as soft as full flex, but it gives a similar type of line variation) and see if you like it. It also takes the con-70 converter, which is probably the largest cartridge convertor right now (capacity is comparable to some piston fillers). Another pen in a similar price range would be the platinum 3776 with a soft fine (either Chartres Blue or Burgounge (sp?) Red). The Pilot SF is softer however.