I know it doesn't help much but I think that's a question only you can answer. Looking at your previous car history, I doubt you'll ever be happy in a Mondeo, no matter how practical or reliable it is. It depends on your attitude to cars; if they're something that enable you to run your life, buy the Mondeo. If they're a hobby for you, buy the Alfa. I don't think a car has ever existed that truly excels at both!
I'm assuming you're talking about the latest (Mk4) Mondeo, in which case I can't speak from experience, however I did previously own two Mk3's (one hatch, one estate). The second one was top spec and fully loaded with options yet still never gave me the same feeling as my 159.
The Mondeos were proper load-luggers. Good to drive (but not by Alfa standards), well put together, cheap to run (130 TDCI) and reliable. Ford customer service & competence was abysmal at all 4 dealers I used, although I don't think that should influence your decision as it seems to be a foregone conclusion with most brands now. Just find a good independent.
The MK3 had its fair share of known issues as well (maybe solved in Mk4) - some of which would be very expensive out of warranty - rear subframe bushes, injector faults.
I bought the 2nd Mondeo on the strengths of the first one, but only ended up keeping it for 9 months because I realised that no matter how practical it was, I would never look forward to driving it. The Mk4 is supposed to be a better car though and no doubt if you head over to fordmondeo.org, you'll find a load of very happy, enthusiastic owners.
My attitude at the moment is that I'd rather have an unreliable car that I love, than a reliable one that leaves me numb. I'm still in the honeymoon period with my 159 though, so I might feel differently about this if/when the big bills start coming in!!
Go and drive both - several times if possible.