As Nekoshema said its really up to you.However, be 100% sure that the seal you are going to use, is used for the right purposes. We use a pentacle for protection, we use it for the elements. It is our symbol. So if you for example use a protection seal, that will surely protect you, but it could interfere with certain spells such as summoning. Your seal, and your intentions HAVE to correspond to one another :)
Also be completely sure what the seal is used for. There are various sources of information regarding Solomon's seals, so be sure that you use the right information when choosing a seal.
Lastly I would also like to warn you in a sense. Solomon was very specific, sometimes he even spoke a little jibberish. He had rules and steps to follow when it came to certain spells and/or seals. For example a wand, had to be cut with one thrust before sunrise from an oak or hazel tree, with no more than 1 years growth. And then Carved before sunset. So if you are going to use one of his seals, be sure to follow any regulations or steps that have been provided with them. (Paraphrased wand example from memory, so some things could differ)
I hope this made sense, and helped :)