You can chose whatever hardware is available, the bigger you go the quicker the trial ends. Would be nice to get a bit more out of it but its a free at then end of the day. If you wanted to continue to mine after the trial it might work out better renting a miner VM from one of the many places online.
There are super expensive VM's on Azure that also have NVidia Tesla P100 GPU's that'll probably get you several KH/s per VM. However, you'll burn through your free trial within a day. Keep in mind that once you use up your free credits, you actually still do get 750 hours of the B1S series VM for free for a year. Now mining on the B1S VM will get you less than 10 H/s but hey it's free and costs you nothing. I do have a different subscription on Azure and therefore get $150 in Azure credits every month. Currently I'm trying to find a good balance of the F-series VM's to maximize my use of the credits, I've occasionally pushed it too far and end up using up the credits way too early and have to wait weeks for the next set of credits. I'm averaging about 200 H/s across all my Azure VM's at the moment. I'm deciding whether it might be more worth it to burn through all my credits in a day with the NVidia tesla P100 VM's, once a month.
Edit: Well after doing some calculations, I'd make about $7-8 in a day if I mined with 4x Tesla P100's. Which would actually make me slightly more money than mining with the more reasonable VM's. The difference is only like $1-2 though. So if I kept doing that once a month, I wouldn't be making much extra in the long run either lol.