I am currently researching the same issue, although I have a "trimmed" Sky service.
Last time I rang Sky - about a year ago, and told them that I was a poor pensioner, the person on the other end was helpful, and talked me through my options carefully and slowly. We reduced the overall package.
I now take as little as possible, but I've kept the sport and discovery stuff.
I do not need Sky HD, (on a 37inch Panasonic). I'm clear about that. The change in picture quality is not worth it, as the Pana sorts out the picture quality, (somehow). However, daughter's 3 year old 40inch Sony does benefit from HD - the basic picture without HD is nowhere near as good as the 1 year old Pana.
So I would suggest Option 1 to be to talk to Sky. As described above, (mixture's advice is always worth listenning to) tell them you are leaving, and find out their best deal from their retention team.
Then, trim down what you take, and figure out the best price.
Option 2 would be to look at Youview. We have one of their boxes in another room, and SWMBO loves it. (In our set up it needs one of the range extending Homeplugs that GG hates so much). It is free, or you can buy add-ons from BT.
Option 3 is the freesat stuff. I know nothing about that.
Option 4 has to be a Virgin bundle if you are in an area with their fibre. I'm not.
If you keep your plusnet deal, on a standalone basis, they strike me as the best in terms of the price/reliability balance.
BT also have a retention scheme, and my Cunning Plan is to talk to them. I take my phone and broadband from them, on a "retention" deal that they did for me about 2 years ago. I can't find anything cheaper than the deal they gave me, so I'll hang on to it. When I ring, I'm going to ask for their best price for broadband, phone and youview with sport. My "I'm leaving" script is based on plusnet prices!