Best: Either my current 2015 Focus ST or my 2003 Neon R/T. The Focus is pretty much everything I want in a car in it's class. The heavier steering keeps it from feeling loose and wooblely. It's just the right size for me. Is comfortable enough for long journeys but fun enough even at sub 30mph speeds. The Neon R/T for the same reasons, down on power but uber fun to drive and came from a time that the entire time I drove it I didn't feel like I was missing out on features. It may have rattled like a bitch but it took every beating I gave it till I moved on. That car had loads of character.
Worst: Three come to mind. My first car a Oldsmobile Acheiva, lots of history in why I hated it and not all of it the cars fault (I didn't want it, my dad talked me into it, said he could get it running, took 2.5 years) and I only got a couple of good months out of it. Geo Tracker, I got it for $300 with 180k already on the clock. I blame it for never really getting to drive my Camaro before I sold it. But it was a panicky decision based on the Achieva dying and I had only gotten the Camaro at the end of fall with the dream of Driving in the spring. But by Spring I knew I needed a real car and both had to go. But I am going to go with my Dodge Nitro. It probably next to my Fusion and Focus leases, the least problematic car I owned. But its a car I really liked the styling but the car as a whole never lived up to it. It had BT built in but without paying for UC I couldn't use it. It was a 4x4 SUV but felt as loose as a car and the rear end was really twitchy even in 4x4 mode (and eventually cost it, its life). It had the 3.7 V6 magnum in it and that thing was worse than my Neon's I4. It's also the car that taught me that I really wanted to be lower to the ground and in a tighter car. Which is why I went Fusion and from the Fusion I wanted tighter and so to the Focus. The Nitro is like the reverse Neon. The Neon you expect so little from and that R/T gave so much more back to me. The Nitro was the first car I got where it was a car I actually wanted and that one was just placid and weak in every point I cared about.