Two very different cars indeed but both good choices.
I would choose the Jag everytime (no sh*t from someone who owns one right), simply because it feels a lot more special. The M2 is a great car but you'll never escape the fact that it's still a 2 series (even if it doesn't share much with the basic car). Speaking as someone who has had those top of their model range sports cars (Golf R, AMG C Class), it's just not the same as a car that is designed top down. Ultimately though it'll boil down to your use case and personal preference. If you are expecting to spend a lot of time on twisty country roads and need a bit more "practicality" the M2 will be the sportier of the two and more useful carrying passengers. But when it comes to long road trips or just rolling around town day to day, you'll enjoy and feel more special in the F-Type purely from the theatre of the engine and appearance.
As far as V6 vs V8... you really need to try them as everyone says different. Both sound amazing and the V6 has the sportier tone but the V8 sounds like a pure muscle car. It's by no means a "lazy" V8 though. My buddy compared my R to his Mustang GT and said it just has a more aggressive feel to it and just seems like its in attack mode vs the lazier V8 of the Mustang. As far as performance... I'll get absolutely SHOT for saying this, but I really think all the people that say the V6 handles better are just sucking on a placebo. They know it's lighter and therefore go into it looking for the feeling. In reality the weight difference is negligible as far as I'm concerned and unless you are really at 10/10th's, which on a public road you never are, I don't think there is any major difference. I even seem the remember that the V6 even has the same size block as the V8, just with two "blank" cylinders (not the best way to describe it but they didn't save weight properly by cutting the whole block down is what I'm getting at). Anyway... I would just say make sure you try both and if you can on the same roads. Get a good feel for them and take your time choosing between them. One big benefit of the V6 will be that you can probably get into a post 2018 facelift model for your budget. Either way, both are amazing cars and no one ever regrets getting either.
RWD vs AWD... I'd say for the V6 RWD and the V8 AWD. Again there are lots of arguments one way or the other, but as you haven't driven for 10 years and are coming from a 1.2 Ibiza, jumping into a 550HP RWD might be a bit too much too soon. The RWD R isn't as bad as some media publications would have you believe, but you can't just mash the pedal and if you get a bit over-excited it WILL bite you. I didn't trust myself to not do that as I'd been driving AWD for 7 years prior to getting the F-Type.
I don't think there are really any MAJOR red flags. A few things to look out for are water in the boot, corrosion on the cross bracing underneath, and the vent placement on the hood.
For water in the boot lift out the rear section where there is a little cubby underneath. Then pull that up and take a look around the battery area for corrosion or any signs of watermarks. No clips or anything, it all just pulls straight up so is something you can check easily at a showroom.
Take a torch and have a look underneath at the back. Not a lot of room but if you get your phone in there and use the flash you can get some decent photos of the cross bracing. Corrosion is very normal and normally its just surface, but some examples can be bad.
As far as vent placement on the hood - earlier cars had an issue with stuck injectors caused by corrosion from water coming through the hood vents. AWD cars don't have this problem and models after... I forget which year? had the vents moved/rubber drip mats placed on the engine. A search on here should show you which are which -
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Each to their own with options but at the very least make sure you get the V6 S. You'll want the extra power and LSD and other goodies over the base model. Panoramic roof is one a lot of people like, myself included. Rear camera is a MUST. You can get these retrofitted but I'd save yourself the hassle.
No major mechanical issues to ask about but make sure the service history is full and correct. Spark plug changes, ,belt changes, diff oil etc at the right intervals. if you find one you like DEFINITELY make a post on here asking for a background check with the plate and preferably VIN number. A couple of helpful guys on here can look up details on the car and find if there are any oddities in the service history/ownership. Also make sure you do a car vertical check of some sort. Another tell tale sign of how much love and affection the previous owner has shown it is the tyres. Apologies if I'm teaching you to suck eggs on this one, but if it has budget tyres on it, it suggests someone has been trying to save money and potentially not looking after it.