IES is better but if you are perusing your b. Tech then you can't be able to prepare for IES. Then you have to go through GATE. For preparation of IES you need a one year complete dedication to your preparation. Just you go through all the topics now very clearly that will help you in for both GATE exam and IES prelims. And it will also give you a good base for your mains. In GATE exam the questions are very comparative. You have to know the topic very clearly.