Welsh is completely phonetic, so there is usually only one way of saying a name. Regional accent might modify it slightly, but that will be very subtle. The only name I can think of that has a NW version and a SW version is Siwan.(SI-wan and SHOO-an, Welsh for Joan)
Many of the letters and diphthongs have no non-welsh equivalents.
You just can't teach some people to get the sound right. You have almost no chance of teaching someone to say Lleucu. The spats I get into are about seemingly easy names like Ceri, Eleri and, as you might have seen upthread, Eirian. They are very popular names, especially in my age group, and the ones I know are from different parts of Wales. I even know a male Eirian and a male Ceri (both from South West Wales).
Some sounds aren't part of the welsh language, so when I see them used on welsh language threads I think 'What?' I'd find it hard to transcribe Paul into Welsh.
Some names completely lose their charm when they are mispronounced. Rhys, Dylan, Bethan and Rhian spring to mind. Some names have been 'anglicised' in S. Wales, where Welsh is not spoken as much. (Aneirin and Eira would generally be Uh-NYE-rin and EYE-ra among non-Welsh speakers and they sound much nicer in Welsh)
If it was a thread on Irish names and someone argued that Niamh isn't pronounced Neeve or Nee-um in Ireland you'd get it, or that Orla sounds different, or that Ciara isn't pronounced Kee-uh-ra or See-uh-ra. Some of the Irish names do get quibbled over - Caoimhe and Saoirse, for example.
This link has some lovely Irish names
Have a look at the www.mumsnet.com/Talk/baby_names/3892523-aoife?pg=7 thread if you think Irish names don't get argued over.
Beware of web pages listing Welsh names. Some of them have some peculiar suggestions.