I have two for different reasons.
One particular roundabout in Stockport Town Centre (near the George pub under the 'famous' Viaduct) I won't ride round it coming from the Edgeley direction to the back of the shopping centre - this is where I was knocked off, and the 3/4 way round put's you in the firing line of a dual carriageway entering the roundabout as the traffic is mostly coming off the motorway and is usually travelling way too quickly. I still ride it every morning in a different direction, and some evenings by coming down the dual carriageway, but I won't go 3/4 round which exposes you to the folk speeding towards the roundabout. It's a disaster waiting to happen, and I eventually was a victim.
The other is Wilmslow Road through Rusholme. There are loads on here who use it, but it's not a route where you can get some speed on - way to risky - I use the A34 as there are less side roads, and very few shops/takeaways etc.
Wilmslow Road is supposed to be OK in the mornings as the shops aren't open, but it's Europes busiest bus route, and then add in students on bikes - no thanks. In the afternoons/evenings then it's stupid. The curry houses are open, there are loads of crazy peds, students on bikes, and the worse parking/driving you've ever seen - it's just not worth the hassle. If you actually want to get some speed on, and some training, then avoid it. Just to pootle along then it's OK, but you can't really relax.
Wilmslow Road is even worse than the A6 in Levenshulme - which is another road I avoid in that area for the above reasons.