Which county? I would suggest that deciding to align to what 'typical genealogists' do is not a good idea if it works counter to (a) your software or (b) your immediate intended audience. (Emphasis on 'immediate' audience as our total intended audience should surely be anyone and everyone - however, surely we should prioritise?).
If your software allows standardisation of place-names to (say) current administrative counties, then that gives you flexibility to overcome issues with another choice of county type for data entry.
You should also consider what the software does with the county names - if it simply prints them out again, there are probably no extra issues from that. If, however, it attempts to map them, then some choices of county types may not work as well at locating the places on maps.
Re the immediate intended audience: While I currently use the contemporary historic county for my British place-names, I am acutely aware that in certain areas, the current (today's contemporary) historic county is getting more out of step with what people living there recognise. On another list, the opinion was expressed that inhabitants of (the English) Birmingham would be surprised to be linked to their historic county of Warwickshire instead of their administrative (sort of) county of West Midlands, thinking of Warwickshire as rural. (I know that the question basically accepts that the contemporary place-names are the ones to use, but 'contemporary' needs to cover today's events).
For what it's worth, I think the county types fall into 3 basic types:
- Historic counties;
- Administrative counties;
- Ceremonial counties.
Concepts like registration counties can be classified as a sub-type of administrative county, though please note that the registration county and local government administrative county for a single place might differ.
Other sub-types of administrative counties include county boroughs (where a municipal authority has powers equivalent to those of an administrative county) and their pre-1888 equivalents of counties corporate (a.k.a. 'counties of themselves'). While Unitary Authorities are reminiscent of county boroughs, they have no administrative county above.
After some thought, I came to the conclusion not to use county corporate for place-names - even though that would no doubt upset my Bristolian ancestors, the people of that city being proud of the 'City and County of Bristol'. There are 2 issues with this name. Where to record it - in the slot for town or in the slot for county? And, while Bristol does not cause ambiguities, other counties corporate do - the 'City and County of Gloucester' is a very different thing from the 'County of Gloucester'. The latter is Gloucestershire, the former the administrative unit covering just the city of Gloucester.
This meant that I could then consistently discard the post-1888 county boroughs, which I regard as a desirable result - I cannot believe that replacing "Dewsbury, West Riding, England" by "Dewsbury County Borough, , England" helps the general reader who might, with no clue from the latter name, guess that Dewsbury was once in Lancashire (perish the thought!)
Ceremonial counties seem just plain odd to use - why would we care who the Lord Lieutenant was? The oddness is emphasised by the fact that several of the Lieutenancies seem to have been appointed in groups - from memory, I think that the same person was normally appointed as the Lord Lieutenant of Gloucestershire, the City & County of Bristol and the City & County of Gloucester - so why not have a Lieutenancy for the whole of the traditional county of Gloucestershire?
In the end, I think there are only two viable choices:
- Historic counties (as seen on pre-1974 maps);
- Administrative counties, adding back in any enclaves of county boroughs and / or counties corporate;
Neither are wholly satisfactory - the historic counties are getting out of step with current events and were never as unchanging as their supporters pretend, while contemporary administrative counties suffer from one place being in several counties over history. For the latter issue, I usually quote Widnes, which has gone from 'Widnes, Lancashire' to 'Widnes, Cheshire' to 'Widnes, Halton District' - the first two county names serve to define where Widnes is, while I suggest that in the last case, Widnes serves to define where Halton is!
I suspect that your personal preference is the most valid criterion!