If you pass in an automatic, your full licence is restricted to automatics (category B automatic). If you pass in a manual, you may drive both. That is a DVSA rule, not a school preference.
Automatic can be the right call if a clutch is a barrier — anxiety, coordination, or you simply know you will drive an automatic afterwards. Manual still makes sense if you will share a household car with a pedal box, or you want the wider licence first time.
Use the filter, then talk to the instructor
On PassNear you can filter for automatic, manual, or either. Dual-trained instructors often have two cars, or they will tell you honestly if they only teach one. Prices sometimes differ. Ask before you book a block of ten.