Seeing as a lot of people have already piped in, I won't be repeating a lot of the info. There seems to be missing information about the differences between Prosk and Sentium, however, and the wiki doesn't explain much other than that they're both MPCs (Multi-Planetary-Corporations).
So, I shall elaborate to the best of my memory.
Prosk is a company based off providing cheap/affordable products to the masses. It often allows its districts to grow into dense, crowded urban places, with little cleaning and maintenance on the company's part. Going off the 'affordable products' ideal, Prosk has designed all the light mechs, which probably require less materials to make, and are thus cheaper (though this isn't necessarily true, and certainly does not reflect in-game). Their mechs tend to look more organic and smooth.
Sentium is a company based off luxury/high quality goods, in contrast to Prosk. According to the lore description for the Front Line map, it can be concluded that it keeps the districts under its control in good shape and hygiene. Sentium mechs may look more angular, though this isn't always true.
In Part 2 of Genesis, Prosk seems to have an advantage over Sentium in armor technology, stating that Prosk has the ability to make 'nano-cavorite' compared to Sentium's plain cavorite armor.
There's a lot of information in guides that got lost when the old forums shut down, so it'll take a while to get the information back up. The current guides don't cover much from the Genesis books, and from the previews it seems like it'd be a good source of info, so if you're really interested in the lore I'd suggest picking it up. I think it's about $10 or a bit less for a physical copy, and $7 for a digital one from Comixology.
Edit - Here's a link to a mirror of one of the most informative guides on the old forums. It's got A TON of information nobody else posted, so dig into it - http://hawken.mirror...erse-bible-hub/ Heh, I remember reading it in the old days.
Edited by sabrehawk90, 23 March 2015 - 04:39 PM.