There are lots of brands and models of ECU's out there.  I won't take the time to list them or even attempt tp rank them.  We carry Link and ECUMaster. We have worked with both brands for many years and their products are of high quality, very reasonably priced and very reliable. Here are some differences to help you choose between PNP options:

MAP sensor - the ECUMaster Classic and Black have a built in 4 bar MAP sensor. The Link does not. If you have a GEN3/4/5 it's usually not a big deal as they come with a 2.9bar/27psi MAP sensor from the factory. But a Gen2 map sensor is only 2.2bar/17psi and can't do high boost. So there is an additional cost.

Wideband O2 - again this is built into the ECUMaster products (LSU4.2 on Classic and 4.2/4.9 on the Black).  You will still need a sensor and a cable, we sell these for $150. ECUMaster can also use an external wideband. Link PNP requires an external wideband. Now you may already have a wideband installed on your car so the additional cost won't matter. But we have recently run into cars using some really junky widebands. Innovate has always been awful and unfortunately we are starting to see failures from the previously reliable AEM wideband. We still like PLX and Zeitronix widebands. 

Datalogging - by now you thought this was just an advertisement for ECUMaster over Link - not so. the Link PNP ecu's have on board data logging memory. Meaning you do not have to have a laptop connected for the ecu to record a log. You can attach the laptop later (about an hour max) and download the logged data. Neither ECUMaster unit has onboard memory, but they do sell a cool device that records to an SD card. I have them one on my MK1 SC and it's really convenient. Plus the amount of memory available is HUGE. Cost is around $200 (I'll get them on the website later today).

Plug and Play type - the ECUMaster uses a pnp adapter box (designed by ATS Racing) so it's a little bulkier looking. But the advantage is that you can easily hook up accessories (like flex fuel) directly to the ecu. The LInk is cool because it fits inside the stock ECU case and looks 100% original to the car. However, to attach additional accessories requires an expansion cable (around $35). ECUMaster has PNP options for gen 2, 3, and 4. Link has PNP options for gen2, and 3 and there are some higher cost aftermarket options for gen4 and even gen5 (about $350 more). Here is another crazy thing...there is an upcoming PNP adapter that can use the Link PNP on a 2GR V6. I'm guessing final price will be around $1000 if you already have a Link ECU. 

Throttle by wire - we are seeing more and more of this option used lately. EMU Classic can do it but requires an expensive external module that probably uses up too many of your inputs and outputs. The EMU Black can do it right out of the box and the Link PNP can do it but needs to be modified (either sent to Link or DIY and void the warranty) or an external module. 

So what did I chose? well a little of everything....

1991 MR2 1000hp 5SGTE  - EMU Classic with the memory card logger

1988 4AGZE MK1 - EMU Classic with the memory card logger - we offer a PNP option for the ECUMaster and the 4AGZE

1978 Ferrari 308 turbo - Link Storm with the external throttle by wire module (today I would just choose an Extreme) - I went for this because I wanted full sequential injection and coil on plug for 8 cylinders

1982 Ferrari Mondial 8 turbo - EMU Classic - I kept the dual distributors and was ugrading from CIS (constant injection system) so even batch fire was an upgrade. If you are going to wire it instead of PNP this is the cheapest option. 

1991 MR2 2GR V6 Turbo and non-Turbo - Link Extreme if doing a custom harness or Link PNP option (contact us directly for that one)

Carbon Fiber twin turbo GTO project - Link Thunder because nothing else runs DUAL throttle by wire on this crazy V12