Most of the reviews seem to say that Off the Record is basically Dead Rising 2 with some improvements and character swap. As such, the consensus seems that if you played Dead Rising 2, Off the Record will seem like a rehash. Since I never played Dead Rising, should I just go for Off the Record?

It depends, if you want the smoothest DR2 experience, get Off the Record. Personally, I find the jankiness of the original DR2 endearing, so if you like your games more on the busted side, buy vanilla DR2. It's also way cheaper too.

What about the story? Is there anything substantially different?

Well, kinda. In Off the Record, you play as wartime photojournalist Frank West in a non-canon version of the original Dead Rising 2 story starring Chuck Greene. Frank is a different type of dude than Chuck and comments on situations pretty differently. Some of the dialogue from other characters is changed a bit, too. Other than that, the story is more or less the same besides the endgame, in which one scene and bossfight is markedly different.

Which one do you prefer? Just curious about other peoples' opinions

I perfer off the record I played DR2 when it first came out and wasn't a huge fan but I just got off the record for $12 and it's great

I do prefer the original, but that's likely because I played it first and because Off the Record is really just the same game. Keep in mind that Off the Record has more stuff in it though, it's got a whole carnival area missing from the main game.

Not that I am expecting ton of characterisation, but who do you guys prefer? Any substantial differences between Chuck and Frank?

Chuck is all serious and is all "GRAHH MAH DAUGHTER NEEDS ZOMBREX" the whole game where Frank West is hilarious and zany. Off the Record is the clear winner there.

OTR was my first entry in the Dead Rising franchise and I fucking loved it. So much that I hope Capcom makes this the canon story. Get it.