Some Collectors collect everything, more often than not though as the collection grows (and space for new bottles becomes a premium) many collectors start to specialize in the bottles they collect. In some cases Collectors will choose more than one specialty to collect. Here are some of the ways collectors specialize.
Absinthe bottles come in a variety of shapes and colors. One of the advantages of collecting Absinthe is that bottles are more difficult to find. So the collection most likely won't overwhelm your display area. Most bottles will be found outside of the U.S., they can be a little more expensive to get (there is added shipping to get them to you) than some of the other specialties but well worth the effort (and costs). When collecting Absinthe you are looking for quality rather than quantity. A large Absinthe collection would consist of only a few hundred bottles (compared to thousands with some of the other specialties).
Some people will collect only Scotch while others will collect only Single Malt Scotch or Single Malt Whiskies in General. There are tens of thousands of Scotch minis available with prices all over the place. Most of the Members of the U.K. Mini bottle club specialize in Scothes so if you do, they are a great resource. You can get a nice collection of bottles in the U.S. but if you are real serious you will want to get some contacts overseas to help you find some really cool bottles.
This specialization can be all over the board. Some people collect only Bourbons, some only American Whiskies while others just collect any Whiskey they can. There are even whiskies from other countries people will collect. (Japanese Whiskies are generally sought after) Some of the coolest bottles you will find are the older American whiskies, they came in different shapes and had some amazing labels. Older Whiskies can be very expensive (costing hundreds of dollars for some bottles). There are also many foreign collectors that love american whiskies so even if you don't collect them , if you get some they can make great trading stock.
Vodka is probably one of the most popular specialties out there. It's fairly easy to get bottles at a reasonable cost in the U.S. but there are many foriegn collectors specializing in Vodkas, Particularly in Eastern Europe Countries like Russia and Poland. There are some spectacular window bottles as well as novelty bottles (like skulls and balls). You will definatley find a wide variety of bottle shapes in this specialization in addition to the many collectors specializing in vodkas waitin gto help you add to your collection.
If you are looking for unusual shaped bottles and bottles with blown glass figures inside of them , then Tequila is the specialization for you. Older Tequilas were pretty basic (although there are some really interesting labels) but the stuff that has been coming out the past few years is amazing. Some of these bottles are a little more expensive but some of them are truly works of art. There are also many collectors specializing in Tequilas to help you with your search.
Gins have become popular to collect in the last year or so. There are many new Gins becoming available all the time as well as lots of older gins out there. You will find that a large number of the smaller distilleries that have been poppin gup make a Gin (on in some cases multiple gins) the only problem is not all of them put the product in mini bottles.
Ceramic Figurals in the U.S. had their heyday from 1960-1980. There are hundreds (if not thousands) of bottles that were made in the U.S. during this time that are available in the secondary market. Very few new figurals are coming from the U.S. but other countries are continuing to put out new and interesting bottles. The best place to see many o fthe figural bottles that are available is at the MiniBottle Library (www.minibottlelibrary.com) . You can find a bottle that represents just about anything out there and that is what makes these popular to collect.
This is only a few of the more popular ways collectors specialize. You could collect only from a specific brand (i.e. Johnnie Walker) , Distillery (i.e. Bowmore) or try to collect bottles from every state (there are distileries popping up all over the country these days) or only from a particular country (Germany has many bottles and quite a few of them have very funny labels). However you specialize (if you choose to go that route) have fun, and make sure to find other collectors, it makes collecting much more fun when you are sharing it with others that enjoy collecting too.