You can use either. This link taken from IRS Pub 463: https://www.irs.gov/publications/p463/ch06.html#en_US_2016_publink1000283280, allows you to use the GSA.gov per diem amounts for both lodging and meals and incidentals for approved travel expenses. The GSA.gov website for these tables can be seen clicking on this link: Per Diem Rates - GSA
You may claim actual expenses if they are not considered lavish or extravagant, but, having said that, the per diem amounts are actually quite generous numbers. (I recommend familiarizing yourself with Pub 463 some as it is the authority for all of these types of questions on deductible business travel).