[Perfectlap]

if you can swing a 2009 Boxster that's the right starting point. It's the all new engine that is the latest and greatest.
Before 2009, if you want to look for first gen Boxsters, find ones that have already had the IMS issue addressed. If not you should add $3K to the asking price right off the top. And get a new water pump in it if its still on the factory original, best practice is to replace every 4-5 years as failing water pumps take down many more engines than the IMS issue that gets all the attention. Once the IMS is upgraded you're pretty much in the clear on that issue because its extremely rare to hear of an IMS failure on Boxster or 996 Carrera that had the original IMS replaced proactively.
If you find one that has had this work done already, make sure it's been a few thousand miles since the swap. This means that the swap was done before any metal ended up in the oil. You want to do the swap when the only thing in the oil is oil.
The really early Boxsters 1996-99 don't really have IMS issues at nearly the same rate but good luck finding a low mileage example. 2005-2008 really don't have IMS issues since they added the non-replaceable IMS bearing that rarely fails, but if you intend to own long-term be aware that these IMS bearings can not be serviced without splitting open the engine....probably not an issue if you're not adding a huge number of miles. Otherwise these are good value if you prefer the styling. Engine wise, the m97 engines in these aren't that much different from the m96 engines in the 2000-2004 Boxsters (according to our resident engine experts).

But overall:
96-99 are essentially the same car.
00-02 are essentially the same car.
03-04 are essentially the same car.
05-08 are essentially the same car.

I would look for the examples with the lowest mileage within each of the above year ranges. Don't pay up for year, pay up for low mileage. Personally if you're going to go with a first generation Boxster the 00-02 S model is the best option as far as engine issues. If you go 987, look for a low mileage S model as well. At this curbe weight, the extra oomph of the S model engine makes a difference off braking and out of slow corners giving it a more lively feel. And the extra ponies are very handy in highway merging and overtaking slow mini vans in the left lane.

p.s.
I prefer the 986 interior, the 1993 Concept Car design was fantastic. Unfornately Porsche stripped it down and made everything in the interior an expensive option. But a well optioned 986 looks sportier to me (which is a bit of a contradiction) than anything else by Porsche that came after in everyone of their cars. The 986/996 interior seemed like a smoother transition from the 911 and 964 era. A bit similar to the 993, especially the seats and steering wheel. The 987 interior was improvement in materials but I don't care for the Audi/BMW sedan'ish feel in a roadster. I'm not a fan of the steering wheel design and the side intakes still look weird to me. The 987 rear end styling is however a huge (as Trump would say) improvement over the 986 in my humble opine. This is all subjective of course.