T4
Until recently I lived in Maidenhead. Access to T4 by public transport is not good from that side. You can take a local train to Hayes and then change to go to Heathrow or the 74 bus (takes over an hour) to central area followed by Heathrow Express to T4 By car the obvious route is M4/M25/Southern Perimiter Road but the motorways can be pretty unhelpful at times so it pays to know the back roads. Even if Airtrack gets built access from that part of the Thames Valley past Slough abd Maidenhead as far as Reading will remain poor.
Long Term parking for business is suprisingly close to the terminal and I have walked it on a couple of occasions (10 minutes). However, cost is such that anything more than a one day trip (not even overnight) and it was cheaper to taxi. I tried the other car park just once - never agin, it's in the back of beyond.
Once inside it's all very gray which I've always put down to a legacy from the BA interior colour scheme of the time when the terminal opened. Prior to the opening of T5 the terminal was becoming seriously congested. It's not worth trying to separate checkin from security from anything else the whole terminal was a zoo. However, it's now more like a ghost town.
Maybe fsmilisrity breeds contempt but I always liked T4. The congestion was a pain and the walk to some gates was a bit long but I never had any serious problems with the layout. The management of the terminal was something else. Quite apart from the congestion stand allocation/changes meant that there were several occasions when I found myself hustling from one end to the other.
As with most BAA terminals I felt the shopping had been allowed to overtake the basic reason for the existence of the terminal and, as time went on and more passengers went through the place and they built more shops so the congention got worse.
The other issue with T4 has always been where it is. If your aircraft lands on the northern runway (and when landings over Windsor are in use you always land on 9L the northen runway) it takes an age to taxi to the crossing point of the southern runway. Then you hold for crossing clearance then you hold again because your stand isn't free and finally you wait for the buses. Bussing and waiting for a stand should currently not be an issue but the rest of it remains an issue for T4.
Arriving has become slower in recent years but that has affected all airports as entry checking has been tightened up. I only had an issue with baggage delivery times once and that was on a delayed flight very late at night.