More opinion than anything else ...
First... I initially missed the word "software for" in the question. After realizing that, I think all 3 of the designs fail at presenting that particular aspect entirely. I thought these marks may have been for a review site or a dealer. I had no clue, by looking at any of the 3 marks, that "software" was the company focus.
Left to right 1, 2, 3....
Which font is the most legible?
1 and 3 are the most legible. The reverse type of 2 (green) is a bad idea and there's not enough contrast between the green and black for that mark to work. I do feel the color choice is poor in all 3. Not because of the hues but because of the values. The green is too dark to be reverse. The purples are too light to be seen as prominent.
Personal pet peeve... using 1 type glyph and expecting it to be read twice. That's not normal behavior when reading and merely makes a mark less identifiable. #2 is using this a bit too much.
Which mark is modern and memorable?
"Modern" and "memorable" are very subjective terms and in the eye of the beholder. There's no rule which one can use to quantify either. In broad, general terms, to be "memorable" a mark needs to be fairly simple and easy to read. While #1 could be okay. If I had to choose one of them, I think #3 fits this best. Whether they are "modern" is another matter. What's seen as "modern" today may not be in 5 years. I think shooting for "timeless" is a better path in the long run.
Which color scheme represents the brand values better?
My personal opinion is that green is hard-pressed to pull off "high-end" or "royal". Not impossible, but takes concerted effort to be done well. Purples and blues are good for that, but not screened, washed out, purples.
Think of trusted services.... financial institutions, emergency services, etc,... blues and purples are most common ... especially blues. I suspect purple was used because if you search the web for "royal colors" you find an overwhelming amount of web sites telling readers purple is "royal". I don't really disagree, but the purple and black designations in these may not be best overall. The black outweighs the screened purples and the "royal" aspect doesn't come through.
Which logo style would work well at small and large sizes?
You can test this yourself by merely reducing the image. I also feel for logo design it's imperative to see forms in one color to get a better sense of balance and unity.
As you can see above #2 fails completely. The contrast is too low and that black box behind "cents" is too tight and reduces legibility. You can also see in the one color versions the name of the brand is the least prominent in all three designs.
While I think the iconography is okay, I think it's merely too overwhelming in #1 and #3. Actually the car in #1 is a bit too obscure to be effective. It could be enlarged to be made more prominent. It's a decent idea, but needs to be fleshed out a bit more.
Sidebar: I also think the name is somewhat convoluted... I get it... "two cents" where automobiles are concerned... but I can't help but think "AutoCents" makes for a better brand, of course then there's the cents/sense issue (this may not be change that can be made, I'm aware.)