Completely agree with last comment ... consistency would be wonderful.
I think the original question was aimed at in-flight service, so I won't bang on about check-in and screening procedures (let's face it, life is too short for that). What I appreciate in flight is basically the following:
1. consistent service that reflects the class of cabin (I truly don't expect a J-class service if I fly economy, but I definitely don't expect economy service if I am up the front)
2. a courteous and friendly welcome by CC at the door (and to be escorted to seat if in First). Prompt collection of coat and distribution of welcome drink, newspaper, amenities etc. if in First or J.
3. a seat that functions and is not dirty, broken, collapsed, tray table knackered, audio not working etc. etc.
4. not to be bothered by perpetual nannying announcements/offers to purchase duty free/join frequent flyer clubs etc.
5. CC that is not arrogant, bullying or grumpy, i.e. with a service attitude. Ok, everyone has bad days, but you are paid not to take it out on the pax. Conversely, we should just have the manners and breeding not to take it out on you.
6. An edible selection of food (I am assuming a reasonably long flight here) that is served efficiently and courteously. A plastic tray hurled at me in economy is not pleasant, whatever the contents. Alternately, on a recent Korean Air long-haul, an economy meal was served with all the grace and courtesy of a first-class meal on United. I could taste the difference!
7. If up front, a reasonable wine list served efficiently and knowledgeably - by CC who have had at least one module of training on wine. Refills served just at the right time.
8. An entertainment system that functions and offers a reasonable selection. Sorry, but if it ain't on demand throughout all cabins, then your airline is woefully out of date.
9. A CC where at least one person is available throughout the flight, as opposed to one where they ALL go off and hide behind the curtains as soon as the light goes out and appear very disgruntled if disturbed (or the AlItalia crew a few years ago who stood around in the galley smoking (yes, you did read that correctly)).
I think that's about it. I don't think it is too much to ask. In fact, I have to say this is exactly the service I got on two flight last month (VS LHR-SFO Upper, and BA LGW-KIN J). Thoroughly professional, cheerful, efficient and pleasant crew who knew exactly how to behave to make a very frequent traveller contented. The worrying thing, as pointed out before, is that (especially with BA and AA) the consistency is lacking - one flight great, the next flight awful.
Final thought: I think we all understand that the glory days of the 80s are over in terms of business travel. Corners are being cut, frills are trimmed. I can't yet say that the business class of today is the economy class of the 1980s, but it is getting that way. On the other hand, there are vast improvements in terms of e.g. in flight entertainment, flat beds etc., that make life better. The whole exercise of air travel is vile and vicious, and this affects everyone, SLF and CC alike. I fully agree that SLF should treat CC with respect and courtesy, rude and arrogant pax (which I am not) are thoroughly obnoxious. On the other hand, CC, whilst there are many things you can't do anything about, such as your airlines' policy on meals, wine choices, etc. etc., a pleasant demeanour and cheerful disposition, and doing the best you can with the tools at your disposal, can make all the difference between a pax coming back for more and choosing a different carrier next time.
Hope this makes sense!