Depends on what you want to experience

Are you (or your bottom) looking for heavier, more of a thuddy flogging? Look for leather or elk, with lots of falls. Looking for a lighter, more stingy feel? Look for fewer falls, made from lighter materials. Keep in mind that the heavier the flogger, the more work it is going to take to flog with, so kepe your own comfort level in mind, as well as your bottom's.

Really the only way to know is to hold it in your hand and use it. Is there a kink community in your area? Many kinksters are also craftspeople, and make and sell floggers. I have custom made floggers, and if you find someone local to you you could have quite a bit of say in how they are made, etc. I wouldn't go through a general BDSM online store, instead look online for places that only do floggers. You might also check EBay, I have seen some really nice ones there

Good Luck !!

There is no substitute for experience!

Unless you personally have tried out the entire line, then I would not recommend buying online.

If you need help I have plenty of toys & eXXXperience!

Even though you have a rabbit flogger, I would highly recommend that you e-mail the fine folks at BunnyFlogger.com.  Despite their name, they do all sorts of floggers.  I had them do a custom flogger for me last year, and it turned out great.

Just tell them that you're a newbie and see what they recommend for you.  In my opinion, you can't have it both ways -- you have to pick thuddy or stingy, because that's how they cut the ends of the leather strips.  Thuddy is more square with rounded corners.  Stingy is more triangle shaped.  I recommend thuddy.  Start with deerskin or something soft.  You'll have to decide which of you is going to be more likely to use it more often, because a flogger is often manufactured to have the handle length be appropriate for the height/arm length of the user.

P.S.  You are 100% correct that most floggers at sex stores are shit.

My very first flogger was from Jeanette Heartwood, purchased from her in her last year of manufacturing them personally.  Unfortunately, the process of manufacturing floggers (from all of the tight wrapping) can render the maker intensely arthritic, so they have to stop at a certain point.  It's the most treasured item in my collection.  I basically told Jeanette that I was a newbie and let her make most of the decisions for me.  She asked a few questions about my height/arm length and what sort of intensity I wanted, what colors I wanted, and then she was off to the races.

Unfortunately, Jeanette Heartwood sold her company, but I believe that the people who took over her business have the same commitment to creating the highest-quality floggers, so I feel safe recommending them as well.  This is the Sony or Cadillac of floggers, if you want a toy that will last a lifetime and perform brilliantly.  (A good flogger makes the user look better than they actually are.)

This article will be helpful to you, to familiarize yourself with some of the terminology.

More advice/terminology that you might find helpful.  You'll be an expert in this subject in no time!