I have both in Mk1, have driven the Mk2 MR2 and the Mk2 & Mk3 MX5's so am fairly up on them.
They are both similar outputs, both are as practical as a bedsit for a family of 6 and are both loads of fun. You can have a factory fit hard top with either as well.
MR2 - loads about, ignore the 1.6, it's pants. The 1.8iS is the model to have really. There isn't a great deal to go wrong with them and they like a good thrashing. Easily converted to forced induction, handle like they ae on rails, provided decent tyres and just buckets of fun.
Need to watch out for accident damage from wifey's spinning them through lack of ability, linglong/viking/lassr tyres or a combination of both. Needs full service history, ideally want an enthusiast. Being 'tracked' isn't the end of the world - it's great on the tack so why not take it there?
MR2. Again, great handling, weigh next to nowt and are a hoot to drive. Early allys have a habit of going porous so look for scabby wheels and flat tyres. Read up on the pre-cat issue, now resolved but not in all early cars. Mr2oc (
www.mr2oc.co.uk) will tell you more. Again, same issues of who's spun it/crashed it etc.
Myself? Dont know, probably the 2 because I'm an MR2 geek but both are hugely capable, great fun and rag top to boot.
Good luck