My choice would be K3, without a doubt, and what I run, with perfect success.
The emerald does batched, semi or fully sequential, will do grouped injector banks, or 8 injectors on 4 cylinder phased in.
Sensors are calibratable, resolution is down to 1% on load speed sites.
Eg my(2wd sapphy) tps buggered on dyno, put on universal one, few presses of pedal and compy keys start to finish fitting get going 30 mins, and cost me £25 for a universal.
The boost control in particular I really like, as it uses TPS pos as well as boost level for control, so is instant at losing boost.
Mine runs like a dream, and will happily do 40mpg+, I also have the fan control on mine, it can control air con fans as well, mine comes on at 95C and off at 92C, sits in traffic all day perfect.
I like the fact it is designed in house, was built in house but they can't keep up with demand, so built at a pukka electronics place, where quality counts, and they are mapped in house, or by agents.
They have been modified to run things like audi 5 cylinder, twin cylinder, a 27 litre rolls royce merlin engined rover sd1, with 24 injectors and two jag dizzies.
Runs coilpack or individual or std coil and points whatever, has masses of trigger patterns that it takes, uses all oe sensors, or aftermarket, can use it to dial in innacurate tacho's via tacho feed adjustment.
It has three maps, mapping costs £280 for all three not each.
Just have a look on the site, they are used extensively on lots of different cars 205/jags v12/lotus the list is endless.
Has been used on lots of different class leading cars too.
Dave has cars trailered over from different countries just for mapping, and if he though you would be better off with a different make ecu he would tell you so, he is that honest and blunt, and has more than enough work.
tabetha