orthography - ー vs small kana vs long kana for writing long vowels

I had thought that for writing long vowels in Japanese, that small kana was mostly used with hiragana and ー was mostly used with katakana.

I was actually thinking of asking whether there were exceptions but then when I looked up a word I'm interested in lately I found all these spellings in WWWJDIC:

• すげー


• すげぇ


• すっげえ



• すっげー


• すげえ


• すっげぇ

Not only are there variants with ー and ぇ, but also え!

In general, how do I know when to use which?

Also do I need to know which is needed to type them? Assume I know how to type them if I know the spelling, but consider also the case where I've heard a new word in speech and don't know the spelling yet. (Please don't tell me that's a software issue with nothing to do with Japanese.)