I've riden Diamondback a lot of times but I've only riden on the inside seats. If anyone has ridden on the outside please tell me what you think.

The inside seats, as you call them, are far smoother than the outside seats. The experience of sitting that far out from the track is well worth experiencing. Try it!

The outside seats are way better because you're more off the track and it's mor thrilling,

Just my opinion...

just give it a try.

I have yet to go to the park when they aren't doing assigned seating. Even on days where business is light. Do they have days where they aren't assigning seats?

Yes. Though it is rare. Oftentimes in the morning, they don't assign seats at first.

Even if they are, if you ask nicely and politely, they will often honor your requests...

I much prefer outside seating...

Pros about outside seating:

Wind rushing in your face, the "off-the-track" feeling, and when you go on the midway turn (I forget what that element is called) you get faced towards the ground. That part is really fun!

I have only rode in the outside seats. When I was there this weekend I was wondering what it would be like in the inside seats.

I just overall love that ride!

I like the outside seats the best due to feeling like you hovering in mid air, but any seat is a good seat on DB!

Pros-You are right on the edge right on the rail.

Cons-Since you're right on the rail, it is a bit rougher.

I notice little difference. You feel a lot more free since you aren't slammed in with the person next to you. It can get a little rough at the bottom of the first two drops, but it's really insignificant. Still the smoothest coaster at the park.

I will say that the hammerhead turn (after the 3rd hill) and the final helix (before splashdown) are a lot more fun since you hang over the edge.

Try going in first thing in the morning, during ERT if possible. They don't assign seats if you get there early enough.

I love the outside seats much better but just like Terpy said they usually will put you on the outside if you ask nicley.

I've asked for a specific seat many times when the line was short, not once have I gotten it. Seems like it just depends on who's grouping.

I have yet to go to the park when they aren't doing assigned seating.  Even on days where business is light.  Do they have days where they aren't assigning seats?

Yes. Though it is rare. Oftentimes in the morning, they don't assign seats at first.

Even if they are, if you ask nicely and politely, they will often honor your requests...

I've also seen it when the lines in the station are empty they will tell people to choose your own seat until it's filled then they place single riders in different row's so the train is filled. 

Everytime I have ever rode DB they gave me the freedom to choose my own seat, I just tell the operator where I would like to sit nicely, and they have always told me, "Go ahead". I will say most of my visits are in the mornings.