Well they are basically the same with some differences between them but usually Light Novel is better since its the finished version. I suggest the LN but you can always read both.
I wouldn't go into "usually" because most light novels I tried were worse than the web novel version. The problem stems is that many light novels aren't just "polished versions" but "editors want this cause this is trend now" or "novel must be changed to not be like the web novel". There was this whole thing about light novels being written by editors instead of the authors themselves. So calling them "polished versions" isn't always accurate. I can't speak for this one though since I didn't read it, just pointing out there is no such thing as "usually",
LN has more girls, one of them appears earlier, another one has different traits, another one loses her most characteristic trait... a secondary character has an interesting background that explains why he is so similar to second's son, there's a new villain (Lyle's "clone")... some endgame plots pop up earlier... overall LN is better but unfinished... (as for the "usually" topic I've only read four LN that are also WN (well five but one of those I've never read the WN) and of the four three are better (I mean Shieldbro LN is SO MUCH better than Shieldbro WN and so is Mistaken as a Genius) and one is pretty much the same...
Reading either is fine, tho I think the beginning of the end is much slower than the LN so I recommend reading the LN as it's less of a grind to the good stuff.
LN Vs WN LN -Has a professional editor go through it checking for redundant points and information (more concise plot points and better narrative usually) -illustrations -new characters and plot branching -polished minute details -censorship in some cases (depending on the target audience or country, less gore, etc) -for ecchi or adult novels there can be the addition of more explicit snu snu rather than implicit scenes WN -unfiltered and unedited work of the author's version of the story -limited censorship (unless the author is posting his work in an r-15 context, certain themes are too dark or law breaking in some cases) -has redundant information or fluff words (Chinese wuxia works on QI are guilty of this with paraphrases like "You Dare! Didn't give me face! Face Face Face!) -Can be discontinued or deleted in favor of the LN version due to Publisher deal
Wow, what a nerd. XD I could hardly stand 2 titles with similarities, yet you read 4 versions of the same book?