Tengu for NPCs that have either a weakness to Kinetic, or a secondary weakness to same.
(Primary damage type against Caldari-derived NPCs, secondary weakness of Serpentis/Gallente and/or Minmatar/Angels and Mercenaries, respectively.)
Machariel for everything else...or just the Machi for both, either ship works just fine with a basic T II fit, although the Tengu really shines with some judicious pimpage (mainly Caldari Navy BCUs in the lows and a complex small-size Shield-Booster. I use a Pithi C-Type Small, and a CN-issue SBA + 4 CN BCUs in the lows--all else, T II. These mods will free up enough CPU to switch the electronic subsystem to the Dissolution Sequencer which increases targetting range to like, 115+ km from 85-90 for the CPU Efficiency Gate.).
Lots of fun to fly either like a big Assault Frigate--turn on your O/Vs "transversal" column, and approach indirectly/spiralling in, hit "orbit" at your preferred range, speed mod on. This is much easier in the Tengu, as you don't have to worry about your whipping about your targets affecting your missiles' accuracy. The Machi, on the other hand, might be considered a bit more forgiving as you can deal with webbies/pointies with your drones. (IMPORTANT: Kill any webbers ASAP in either case!)
You absolutely cannot AFK either one, though, that could hurt...a lot. Not a big thing, in practise though, as these both kill shit so fast that you may well be flying back to base for the next mission before you'd even consider going AFK in the Rattler for the first one.
After those two, anything else is just too much like work.