The best was having our garage converted into a bedroom for my son so we could separate our (then) warring teenage sons.
The worst, without a shadow of a doubt, was when we had our bathroom refitted a few years ago. We went to the ideal home show and chose a very fancy, absolutely amazing shower/bath unit. It had four different types of shower, the thing in the bath that makes massage bubbles (both husband and I are having a blank moment and can't think what they're called
), mood lighting, blue tooth, radio - it was just amazing. It cost us £2,000.
Except it never worked. It was totally unsuitable for the bathroom, despite the promise that it would be perfect. The electrics never worked, the bubble thing never worked, the aromatherapy bit never worked. It was a nightmare.
In an ironic turn of fate, there was an issue with the way the toilet had been fitted in the bathroom and it had been leaking for two years. Eventually, the bathroom floor couldn't take the weight of the accumulated water, and we ended up with the kitchen ceiling all over the kitchen floor because of it.
Our insurance company were amazing, and because the water pipes went under that awful bath, and the panel was an integral part of the unit and couldn't be removed, they had to literally rip our bathroom out, right back to breeze block and rebuild it. We now have a lovely walk in shower and lovely toilet/sink unit.
I've never been so pleased to have a home disaster. I thought we were stuck with that awful bath for life.