There is always the DIY route. FT232H/PL2303/CH340C/HT42B534-SO16/STM32F042F4P6 + MAX3245 = win.
EDIT: Now that I read that you DIY route with more attention, it will work, although I still keep what I said below.
Prolific chipset converters are wonderful - when they work. They're one of the most problematic ones available and require close matching of the Prolific driver to your system's current service level. Widows updates are known to break Prolific drivers from time to time.
Converters based on the FTDI chipset generally have the least number of issues. One great advantage of FTDI is that if you move the adapter to a different USB port, it generally will not change serial port numbers (but that you guys know a lot more than me).
The Keyspan USA-19HS is the only thing I've ever been able to get to work with all of the devices I needed to use (PLCs, shipping scales, network equipment, Renishaw QC10 Ballbar System, the list goes on). This is because it has an FTDI chip and based around the TI 75LV4737A, so it has a real serial processor, as opposed to a lot of the other brands/models, which use a Prolific chip. The Prolific chips are just emulators and only work about 75% of the time.
I used basically from the generic black smoked plastic adapter with unmarked chips to Belkin ones based in the Prolific chip. They are good for switch connections (Cisco Rollover cable and most networking).
Does this adapter have full HW handshake?
I am always looking for additional suppliers for these adapters, as we never know if a manufacturer will simply kill their models.
I am currently using this Trendnet TU-S9 that has full HW handshake and it works really well, but I never know if/when this will last in production...
The Tripp Lite / KeySpan have HW handshake yes.
Its based on the TI 75LV4737A Multichannel RS232 Line Driver/Receiver.