Linguistically, the sound in the English word "cake" is a diphthong
[ej]. In most languages which use the Latin alphabet (including Latin itself), it would be written as ej or ei, more often the latter.
A very similar sound is written as
[e] in the International Phonetic Alphabet. This is a monophthong as opposed to a diphthong, but in English the distinction doesn't really matter (as opposed to in, say, Hawai'ian). Most Latin-orthography-using languages write this sound as e, or as é if they need to distinguish it from other front mid vowels; é is probably as close as you can get with a single letter (and may be familiar to English-speakers from French loans like né, fiancé, café, résumé).
I don't know of any language except English that would use any variant on the letter a for this sound.
[ej] is a high-mid front vowel at heart, while a almost always indicates low vowels of some sort, and usually back ones at that.
1) tæta 2) tāta 3) táta 4) tåta
To linguists and speakers of Old English, æ is the vowel in "cat". ā generally indicates either a mid tone or a long vowel, while á generally indicates either a high tone or a long vowel, but neither would sound like
[ej]. And å is usually somewhere between the vowels in "awe" and "phone".
If you've got your heart set on using some variant of a, you should probably go with ā. The idiosyncratic transcription system used by the American Heritage Dictionary uses ā for
[ej], so some monolingual English-speakers may be familiar with it. But expect most readers, especially those who know any non-English languages, to pronounce it like the first vowel in "father".