What do you have at the moment, and what experience do you have?
How technical are you?
What dish setup do you have?
Do you want to punch in codes, do you have or want a programmer and cards?
Do you just want to watch telly, or get into it more as a hobby?
Where are you and what sats do you want?
What sort of channels do you want?
Think about these things. Read Wotsat reviews and ads. Check online reviews. See what other folks on here have, and what their experinces are. Go with the crowd. It's safer and cheaper in the long run. Consider support, images etc. How easy are they to patch and maintain?
Maybe come up with a shortlist of three. Know all the pros and cons of each. Find a typical price for each, and then look to see what special offers you can find.
After about six weeks, you should know what you're going to do.