We”re talking about very different products.
1. Otzar Hachachma – contains over 100K scanned books, with search capability. Each year there is a new version with more thousands of morebooks. This includes options for all the books from certain publishers, which one must pay extra for. The main three publishers are Oz VeHadar (includes Mesivta, but no printing on anything), Mossad Harav Kook & Machon Yerushalayim (I think no printing). They have a new really nice product called HaMefaresh which gives all known commentaries, discussions, tshuvot related to every sentence found in Gemara, Rashi & Tosafot. IMHO, this gives really high added value.
There are two possibilities of using this –
1) purchasing the product. I priced this with the Book Week discount + the above three publishers + HaMefaresh (you cannot purchase HaMefaresh without Otzar HaHachma) – came out to over 10000 shekels (I am zocheh to live in Eretz Yisrael and pay with the local legal tender). The yearly upgrades are also around 1500 shekel/ per year. Unless one will use this basically 6 days a week, I personally see no economic justification for purchasing this.
2) Use the online version – which one purchases rights for a day, weeek, month, year or 10 separate days. The cost for a day is 20 shekel. Access to books from the above publishers cost a few shekel per day. HaMefaresh 15 shekel/day (you don’t need to also pay for the basic 20 shekel). You don’t pay for yearly upgrades, they come automatically online.
I”ll just add an anecdote, when my 6th grader asked a really good question on the Gemara he learned, paying 15 shekel and finding with him several answers with the Mefaresh was a pretty good Geshmake.
Bar-Ilan – honestly, an excellent product. The price point is pretty reasonable. There is a rich set of Seforim + Shut”im + Encyclopedia Talmudit with footnotes (costs more). The search engine is probably the best in the business. The seforim are shown in text mode, not as the original page. This has advantages – allows for clean copy-paste, allows for quick find within the text (think of looking for a certain sub-topic in a long shu”t). This also has disadvantages – I find it difficult to “learn” without the original look and feel. There are yearly updates, more books. Updating once every few years is pretty reasonable.
HebrewBooks – Free online repository of about 100K scanned books. There used to be a hard drive version for sale ($100), but from what I can tell this is no longer available. There are lots of old books, but also a reasonable amount of current or near current books. There are two sites, the regular one and a beta site, with site differences. The regular site has Shas Nehardia, which can be downloaded. The beta site has a pretty good Tur & Shulchan Aruch (no download). Each book can be read online or downloaded as a PDF. From my experience, one can find some real gems on HebrewBooks and its all free.
Sefaria – Useful for online copy+paste and has some parts have a translation. The translations have plenty of mistakes – but it can still be useful when you need it.