I won't pretend for a minute to be a saddler but I do know what I like. Being tall I know from experience how difficult it can be to get a good saddle that fits. Here are some pointers about the types of saddles that are available and features of saddles that could make the difference between a comfortable ride and one that puts your safety at risk.
Types of Saddle
Broadly speaking (in the west) there are two types of saddle - the 'English' Saddle and 'Stock' Saddle, better known as the 'Western' saddle.
English saddles are used for different 'types' of horse riding all over the world, not just in the UK. There are many styles of saddle with different features for the different types of riding activities such as eventing, dressage, show jumping, hunting, racing, polo and everyday hacking. For example, dressage saddles are designed in such a way to offer excellent support for the rider's sitting position.
Western Saddles were originally designed for use on horses in cattle ranches - they differ in looks from the padded English saddles which tend to be more flat, by having a very distinctive horn on the front of the saddle which was originally used for roping cattle. The western saddle doesn't have any padding and is used in conjunction with a saddle blanket.
So the type of activity a rider engages in will determine the saddle(s) they need. Most importantly a correctly fitted saddle for horse and rider is essential to ensure comfort and optimum performance. General purpose saddles are available to cover most riding activities except racing but if you intend specialising or competing at a high level it would be advisable to get a specialised saddle accordingly.
Picking the right saddle
The length of the seat and the rider's leg position will make the difference between a saddle being comfortable or not and it will affect balance and ultimately safety when riding. There are some saddle features to consider and some of these are detailed below but generally speaking the only way to ensure proper fit and comfort is to sit on it and if possible take a ride using it before you buy!
If you have long legs it is going to be more difficult to find saddles that fit you. Firstly, if you've a long hip to knee leg length then you will end up having to have a very 'forward cut' saddle to accommodate your leg, with short stirrups. The most forward cut saddles are cross-country saddles or event saddles. The degree by which a saddle is forward cut can vary tremendously so again try before you buy.
The next consideration is down to personal preference - what size and shape blocks and thigh supports are best for you and your chosen discipline. The block is the padding that falls behind the rider's lower leg, which helps to keep it in place and stabilise the rider and knee. Thigh rolls are the padding on an English saddle that is right under the knee and in front of the thigh that again helps to give the rider more support.
One good feature of quite a few synthetic saddles is that you can adjust the position of the blocks because they are attached by velcro. However, with these adjustable blocks you need to have a second flap rather than single flap over the top to cover the Velcro. It is worth bearing this in mind - you may want to determine whether you want a single or double flap first (see later in this article) before you make your mind up about adjustable blocks.
Most single flap saddles come with thigh rolls. The idea of these is not so they trap your thigh; they shouldn't rest against your thigh when you sit in the saddle. They are only supposed to come into action if you shift forward against them or if you lean against them when galloping. Thigh rolls do come in varying sizes; smaller ones can be seen on the Momentum saddles or larger ones on saddles from Antares or Devecoux - these tend to be custom-made - at a price.
Many saddles have integrated calf blocks. These are positioned on the back of the flap i.e. behind the calf. Personally I find that if these are under the flap of a double flap saddle the shape is often too softly undulating and the block actually pushes your calf away from the saddle instead of 'blocking' it in. As a contrast calf blocks on a single flap saddle very much act as a barrier and you know when your leg hits them.
Now for the single verses double flap debate... having ridden in both types of saddle I prefer single flap saddles although they tend to be more expensive. My reasoning for this is that the blocks on a single flap saddle are on the outside so they are far more defined and therefore give more feel. The reality is that the degree of 'feel' through a single flap is greater as you are actually sitting closer to the horse. However, some people prefer double flap saddles for breaking in youngsters for example because with a double flap young horses feel less movement from the rider and are less likely to panic.
Now for something riders often don't appreciate about close contact saddles. It is important to understand that close contact saddles use foam instead of flocking in the panels so they cannot be adjusted by re-flocking or topping up the flocking as one would normally do from time to time. It is necessary to make adjustments to fit using saddle pads instead, which come in many different types and sizes. The set up at the pommel is also slightly different so that you sit closer to the horse. It makes a difference to your ride so if you get the chance, sit in a non-close contact saddle; then sit in a close contact one so you can assess the difference yourself.
A misconception is that all single flap saddles are close contact and double flap saddles aren't. This isn't actually true - you can get single flap saddles that aren't close contact and double flap saddles that are close contact however they are quite rare... worth a hunt if you feel strongly about it though.
So, to sum up - a saddle fit for the purpose and fitted well with the size and shape features you want will make a significant difference to your (horse and rider) comfort, safety and performance - don't jeopardize this. Buy good quality saddles and use a saddler that is an expert in their trade.