It is always advisable to shop around as many companies as possible when looking for car insurance. You may even find that your lowest quote could be around 50% of your highest quote.
The internet can prove very useful for finding quotes, as there are some sites now that will process your details online, and return with a list of the cheapest quotes for your criteria.
Obviously you will want to go for the cheapest quote; however the policy should be looked at closely to ensure that the excess that you have to pay in the event of a claim is at an acceptable level. Also make sure you have extras such as windscreen cover etc.
You may also want to ensure you have heard of the insurance company, or ask around to find out if anyone else has experience of using them.