Various factors to consider:

MONEY: They say money makes the world go around. Well, in choosing a blind it is important to realize you are choosing a feature in your house you will have to live with for a long time. Obviously your financial ability does have the final say. BUT as I always advise clients rather go for the better choice and do one a month. Rather do that than choose something you are unhappy with later.
COLOUR: There are basically two colour ranges in home decorating, namely blue and brown with white, black, pink and purple the exception. Which one do you prefer and what is the basic colour range of your room. To determine the room’s colour range, look at your floor and walls. One doesn’t change these that often. Some furniture like antiques can also help to determine this.
STYLE: The answer here can best be determined by answering some questions: Do you want to be bold? Do you want a contrast or do you want the blind to blend in? What is the style of the furniture, wall hangings and other features in the room. Also do you want a cottage look, a modern look, a “cool” room or a “warm look”.
FUNCTIONALITY: Children, dogs and cats bring different questions to the front. The basic question is how will they “interact” with the blind. The bottom string of a Vertical blind and a big dog normally do not go well together. So does a small child and a 25mm venetian. Obviously if they are well trained it will not be a problem.
Heat, sun and dampness are other factors. Dark coloured Wooden Venetians will fade easier than the lighter ones. An aluminum Aluwood blind will also fade less then the wooden ones. If heat and sun is a serious question you should maybe look at our Plaswood alternative. These were made specifically with extreme heat and dampness in mind. Here it is worthwhile to consider a Blockout Vertical blind.