The only possibility it can be wrong is if the transliteration itself will change the meaning so in my opinion, all the spellings mentioned above are correct.
However...
Allah should start with a capital as it's a proper noun. This is why I find the following sufficient:
InshaAllah
Insha-Allah
Insha'Allah
Insha Allah
Nevertheless, some care should be taken for those who may be unaware of the word or learning it new by:
- not using a single 'a' like Inshallah making it sound like In-Shall-Laah
- not over emphasising the actual Arabic letters and pauses In-Shaa'a-Allah
As for the meaning, even though it's closest to the actual pronunciation anyone can come up with variations of how it might be perceived and end up with a different meaning. For example the wordقلب (Arabic for 'Heart') can be written as "Qalb" but if a person goes too much into it then there's so many issues:
1) In English, the letter "Q" must be followed by a 'U' so in respect it must be transliterated as "Qualb" but now it will be read as قولب changing the word completely
2) There is no ق in English so technically "Qalb" will almost always be pronounced as "Kalb" كلب meaning "Dog" so no amount of punctuations and symbols will compensate for that
In summary, I take you back to what I said in my first post here:
[quote]Spell it however you feel is closest to the way it sounds in Arabic. For example, in Malaysia, they spell it like insyaAllah where "sy" is "sh" so in that country, it would be better to spell it the way they pronounce the words.

