Yeah, Yeah... Old topic I know, but still an ongoing topic for new and old hands alike.
"All metal or PTFE lined" along with "Bowden or Direct drive" Those are the questions!
This is a very unusual hobby, quite literally every possible modification, upgrade, printer setting, slicer setting, bed adhesion issue... Basically anything that can be altered at all IS SUBJECTIVE to the individual!
Forget printer brand, filament brand, model, clone, genuine etc.
Just what works for one person and gives outstanding prints may not work as well or at all for someone else with an identical setup.
There are just too many variables - Ambient temperatures, air pressure, humidity, geographic location, age of filament before you buy it, shipping and import method of filament, batch to batch variation of filament & the list goes on an on!
Compared with the laundry list of setup and printing problems to choose from these questions are surprisingly easy to answer!
Firstly: Bowden or Direct drive extruder.
A. Personal preference of the builder/user.
B. Suitability for your majority printing work.
I'm not starting an argument about which is better because neither one is! They both have advantages and disadvantages.
Bowden = faster overall printing speed before undesirable aberrations start to become noticeable
Direct = Slower printing speeds, but more suitable for flexible materials and easier/faster setup especially for newbies.
Personally I use a Bowden setup, mostly because I need good quality large format prints in the shortest time possible, i occasionally use flex filament but not often enough for a direct drive printer to be worthwhile investment (and with a little tweaking can still get very good results!)
Secondly: PTFE lined or all metal
This comes down to one question alone!
Do you intend printing exclusively with materials that require hotend temps above 250 °C?
If the answer is "No" do not waste your money on an all metal hotend!
Buy a couple of good quality plated brass nozzles and high quality Bowden tubing or heat break liner (and still have change for lunch and a pint or two on your way back from the shop)
Simply because getting them to work properly for lower temperature printing is nothing short of an absolute "pain in the proverbial"!
On more than one occasion I have been sucked into the hype that all metal is an "upgrade" from PTFE and quite simply it just isn't!
Most of the companies that market them as an all round upgrade want only one thing your hard earned £££! So instead of marketing them as the correct hotend for high temp printing they market them as a general upgrade part. Which isn't the case!
Now if you think that you may want to try out a little ABS or nylon, even an occasional high temperature print here and there then a much better solution is to buy high quality professional PTFE liner such as the Capricorn XS series.
For normal printing below 250 °C will last 3x or longer than a standard PTFE liner and is also safe to use up to 300 °C for short periods and costs just a few £s more than your regular liner!