Romanization styles...

I know that each language written in Cyrillic has their own form of romanization, but is there one true proper way for each language? I know majority of people use what they were taught, or what seems right to them. I have my own form of romanization (I'll post it at the end), and I use it because it makes pronunciations easier for me to figure out. One thing I'd like to know, why in some romanization styles is the letter "Я" romanized as "y"? That confuses me, because the style I'm used to uses "Ya" as the romanization of "Я". Also, is it necessary to memorize every romanization style? That sounds like a chore! ;)

My form of the romanization of Bulgarian Cyrillic is (Letters in Bold are vowels):

Аа - Aa
Бб - Bb
Вв - Vv
Гг - Gg
Дд - Dd
Ее - Ye, ye, e
Жж - Zh, zh
Зз - Zz
Ии - Ii
Йй - Ii
Кк - Kk
Лл - Ll
Мм - Mm
Нн - Nn
Оо - Oo
Пп - Pp
Рр - Rr
Сс - Ss
Тт - Tt
Уу - Uu
Фф - Ff
Хх - Hh
Цц - Ts ts
Чч - Cz cz
Шш - Sh sh
Щщ - Sht sht
ъ - Uu
ь - Ii
Юю - Yu yu
Яя - Ya ya
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My form of the romanization of Russian Cyrillic is (Letters in Bold are vowels):

Аа - Aa
Бб - Bb
Вв - Vv
Гг - Gg
Дд - Dd
Ее - Ye, ye, e
Ёё - Yo, yo
Жж - Zh, zh
Зз - Zz
Ии - Ii
Йй - Ii
Кк - Kk
Лл - Ll
Мм - Mm
Нн - Nn
Оо - Oo
Пп - Pp
Рр - Rr
Сс - Ss
Тт - Tt
Уу - Uu
Фф - Ff
Хх - Hh
Цц - Ts ts
Чч - Ch ch
Шш - Sh sh
Щщ - Sh sh
ъ - Omitted
Ыы - Ii
ь - Omitted
Ээ - Ee
Юю - Yu yu
Яя - Ya ya

*Combinations of "-ий", "-ый", "-ии" are romanized as "i".
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My form of the romanization of Ukrainian Cyrillic is (Letters in Bold are vowels):

Аа - Aa
Бб - Bb
Вв - Vv, Ww
Гг - Hh
Ґґ - Gg
Дд - Dd
Ее - Ee
Єє - Ye ye
Жж - Zh zh
Зз - Zz
Йй - Yy
Ии - Yy
Іі - Ii
Її - Yi, yi
Кк - Kk
Лл - Ll
Мм - Mm
Нн - Nn
Оо - Oo
Пп - Pp
Рр - Rr
Сс - Ss
Тт - Tt
Уу - Uu
Фф - Ff
Хх - Xx
Цц - Ts ts
Шш - Sh sh
Щщ - Shch shch
ь - Omitted
Юю - Yu yu
Яя - Ya ya
' - Omitted