Which bank is best?

<scratches head>
You bought a £250k car? But wouldn't pay the small fee to transfer the money via CHAPS?

First direct wins the MSE annual banking poll with such regularity, I wonder they don't rename it and just have the rest compete for second place.
tesco now runs their own IT systems. It is the only mainstream one which runs standing orders over weekends... almost like it has joined the 21st century.
sainsburys uses some ex-hbos systems and some others I believe. Beyond that, nothing special.
Lloyds /tsb (currently, not for that much longer) / Halifax / bos are all on shared IT systems.
hsbc always seems inflexible to me. For basic stuff it works.
marks and spencer is a rebrand of hsbc, similar strengths and weaknesses.
santander has apparently improved its customer services over recent yes, and my limited interaction with their select service did what I needed.
YBS / N&P offer basic, but generally fine services from what I've experienced. 
Nationwide seem competent from what I've experienced. 

Ive got accounts with almost all of the above. I tend to use them for their strengths, mitigating any issues. I'm not advocating this approach for everyone.

Coop, rbs, Barclays I've not experienced.

If anyone these days has only a single account, or just accounts on one IT system, especially people 'sophisticated ' enough for p2p, then I would suggest considering having at least one 'emergency' account. Whilst the 3+ days of the rbs issue might be unusual, there will be more outages in the coming months or years, so a little diversification might be sensible.

While I initially had difficulties with Santander security blocking things many years ago, an account change to Select and perhaps other changes have made it trouble-free for me for P2P and other investing transactions and the 100k Faster Payments limit means no limit in practice for what I do.

First Direct themselves are good but their security team is HSBC and they are grossly excessive. For example, it was cheaper for me to do some foreign exchange transactions in units of up to £300 so I phoned FD to confirm that it'd be OK to do that. Next week on an unrelated thing I was transferred to the security team which proceeded to tell me that they were closing my current account and changing my offset mortgage to a non-offset one because of repeated transactions. One complaint later and they had listened to the call and reversed those two but left in place a block on HSBC offering me any credit services. It appears there's a you will suffer if referred to us policy in practice if not on paper. If FD had their own security team they might be fine but given the risk presented by the HSBC team I'm not keen. The FD Faster payments limit is actually £20k, not the HSBC £10k, or was a few years ago when it was also still documented as 10k.

I've had no security contact or blocked transactions with NatWest. No contacts makes them the most friendly of the lot so far as I'm concerned. The current 20k/day/transfer limit is sometimes helpful.

So of those I've experience with, Santander and NatWest are a couple that I think do decently well for what I do.

Don't have only one current account. There's no need and you can protect yourself from assorted mishaps by having at least two.

Smile (cooperative) have been pretty good in the past with large transfers.  I've done £95K and £40K ones with no-hassle beyond a five-minute phone call with their fraud team.  Extremely quick off the mark as well. I got a phone call within about 10 seconds of attempting the £40K one. 

Interest rates are absolutely rubbish though.