I have no experience in learning online, since I learned in ulpan here and in EY and on the street there. However, I hear great things about Nefesh b’Nefesh, and have had several acquaintances make aliyah through them. If Nefesh b’Nefesh recommends them they’re at least adequate, but if you still have questions maybe contact them directly and ask if there are other options they can recommend.
BTW, no course, online or otherwise, will help you walk out of the airport and instantly be able to function like a sabra. You have to actually be there and using the language on a daily basis. and you have to put yourself in situations where you have no choice but to speak Hebrew (not so easy, since most Israelis are eager to practice their English on you). Try not to get encapsulated in the English-speaking ghetto. It’s very easy and you’ll never learn Hebrew.
And make sure you can read, if only for the street signs and other practical stuff, and to even eventually read a Hebrew language newspaper.
Good luck!