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I know this subject has been covered many times over the years as I have been trawling through the posts, but have we arrived at a "this is the best, forget the rest" for the DIY budget?
Apart from technical suitability where some work with Jaguar but others don't, it really depends on what level of diagnostics you are looking for.
For a simple reading of Pxxxx (Powertrain) Codes, almost anything will do. Many of us with iPhones use TorquePro because it's cheap and portable. If you want the other extreme of accessing all the data from all the modules then your needs are more towards Jaguar SDD or Autologic.
Apart from technical suitability where some work with Jaguar but others don't, it really depends on what level of diagnostics you are looking for.
For a simple reading of Pxxxx (Powertrain) Codes, almost anything will do. Many of us with iPhones use TorquePro because it's cheap and portable. If you want the other extreme of accessing all the data from all the modules then your needs are more towards Jaguar SDD or Autologic.
As already pointed out, the near perfect budget solution is a cheap ELM327 device supplemented with a mobile app like TorquePro. It only covers standard OBDII, but it works on virtually all cars, covers pretty much all of OBDII (fuel trims, standard P codes, reset, data logging, etc.). It is also great to get a sense of what a scanner does. And with the expense involved, it is a no-brainer. Just get one, even if you get something else later.
A big step up from that is the handheld Jaguar/Land Rover scanner. These tend to cover most modules for most JLR models. The more popular seem to be iCarsoft and Foxwell. The software can generally be updated through a USB or SD card setup, but updates tend to focus on supporting new models as opposed to fixing existing problems. For typically less then $200, you get what you pay for. These devices are good, but not great. They tend to have lots of general claims covering all supported modules in aggregate, but lack in specifics to our cars, especially what feature is supported for what year. For example, the Foxwell device can somehow get diagnostics code from the body processor during a "scan all" function, but not when asked specifically. Vendor support is generally near nonexistent, and the timeline for fixing this bug is probably never. Of course you have to weigh that against the cost of a visit to the dealer and decide. These devices read all trouble codes for all modules (great for doing a search later), can show raw data and graph it (think individual wheel speed, etc.), reset codes, and perform special functions (like pair keys or reset trans adaptations). Not without bugs/gaps/problems but largely worth it overall if you specific model year is supported.
The overall best in terms of coverage is the "factory" software IDS/SDD with a corresponding USB cable. There is a wide variety of versions and, let's say, origin. Ranging from the $200 clone cable and "pre-packaged" software image, all the way to a proper Mongoose cable, properly licensed software and subscription to the online service for many times that budget. SDD runs on a laptop and was designed for Windows XP or possibly even before that. It is fairly bulky, slow-ish and generally unfriendly to the new users, but it supports "everything" in the sense that SDD is what pro shops (like dealers) used. The complication in that "supports everything" is that some of these features require downloaded packages from the subscription service (think ECU flash images, etc.). The good news is there has not been anything new for our cars in years, but whatever SDD path you take needs to have these images available if there is ever a need to do serious "programming".
So, no, there is no "best, forget the rest" but more like a range of options.
To my dated/superficial knowledge, TorquePro is Android. IOS folks mention Dash Command. I am sure there are others. The key is that the software is meant for a generic ELM327.