Okay so two of my close friends are owners of a Passo and a Swift respectively, I'm going to lay down some pros and cons I noticed in both of them, please not that these are purely based on my own opinion and of course you might have experienced otherwise.
The instruments in the Swift are very well laid out, everything seems in it's place and you have a comfy feeling, the front seats of the Swift seemed a better fit and they actually hold you in place compared to the Passo's front seats, although I did notice that Passo has more room at the back, Swift seemed a bit cramped when it came to rear. The materials used in the Swift outrun the Passo and play a big part in the overall feel of the cabin.
Comparing the wind and road noise in the two cars puts the Swift ahead which was much quieter. What surprised me was the constant rattling noises in the Passo, it felt as if the oddly placed Tachometer will fall from it's place any minute. Creaks were to be heard from the dashboard of the Passo as well, while it was totally the opposite in Swift.
When it comes to handling, the Swift is streets ahead of the Passo. The swift felt more responsive, the steering was precise and firm, has excellent resistant to crosswinds (the Passo was pathetic with crosswinds), the Swift felt very predictable. However, the Passo is equipped with Airbags which gives it a little advantage in the safety category, the ride of the Passo was a bit harsh.
When it comes to performance, the Swift takes the lead no matter what anyone says. The gear ratios are quite high in the Passo and this blunts performance inside the city, the transmission of the Passo was jerky and not a pleasure to drive at all. Even the engine is far from being the smoothest on the block. On the other hand, the Swift was a breeze, the engine felt more responsive and eager. One other thing I noticed with the Passo was how it's engine transferred so much vibration into the cabin, something just didn't seem right, and I've noticed this in more than one Passo.
In the end it all comes to personal choice, if I was to choose between the two cars, I'd go with the Swift, however I'm not much of a fan of both, if one spends around 900,000 and buys a USED JDM Daihatsu Boon, then it's better to buy a 2000+ Honda Civic and spend some money on bringing it into shape, that will be actually worth it.
I stick to the famous phrase, Built Not Bought.