Travelling from the St. Helens area, I prefer Manchester Victoria - it is more convenient for the city centre -- although if connecting onto Metrolink, Deansgate is even better. The problem with Piccadilly is that our trains can only use the inconvenient Platforms 13 & 14, although it is the best station for onward connections to Hope Valley, Buxton, Sheffield, etc.
Oxford Road is inconvenient for much of the city centre; it would have been useful many years ago when I was at Manchester University - but there were no services from St. Helens at that time.
For me, the now closed Manchester Exchange was even better. It had easy (but a bit long) connections to Victoria, walking along Platform 11 Middle, and was slightly closer to the city centre than Victoria. The original Victoria was neglected and in poor condition , but the platform layout was much better than what we have now - 6 through platform roads. At the current Victoria, Platforms 1&2, and the Metrolink platforms are fine, but - particularly Platforms 4 - 6 are dark, gloomy, poorly lit, and unwelcoming.
Piccadilly Platforms 1 to 12 were fine, but have been spoiled by fitting barriers. It makes it less convenient for changing between trains, and the concourse area has become much more draughty due to open spaces above the barriers.
Manchester Central was a nice station, but anything but central for the city centre -- perhaps only really convenient for the areas round the city hall and one end of the Deansgate shops. Also, by the early 1960s, it always seemed a bit bigger than was really necessary.
As for London stations, Euston is the one I first think about, as it is the one served by the WCML. Unfortunately, I also think that at platform level, it is a gloomy depressing hole, and the concourse area is congested and poorly designed. Of the other London termini, since I worked in London many years ago, I only use them very occasionally. I used to like Paddington, Kings Cross & Waterloo best. St. Pancras used to be O.K., but the domestic side seems a bit of a mess since the real side was converted to "International". And Liverpool Street was not "improved" by rebuilding.