Hey nazar,I will be happy to answer your travel queries from my experiences 😊.
*both the places (kerela and Shillong)are great for a 7 days trip but it depends on the location you live .if you live near North India or north east ,then Shillong could be your decision and if you are from middle and south parts of India , kereal is prefferably fine . although you can absolutely travel anywhere,this is based on the exertions of trip .
*Shillong is famous for several waterfalls, parks,people, limestone caves ,orange honey ,rolling hills and quaint land form . it's also knows as Scotland of india .
and also have parts of most beautiful rainforests of India.but since the place has not much access to transportation,trains arnt availlable and flight with long duration are availlable.
*kerela too has many things to offer like ecotourism, beautiful backwaters,unique culture and traditions,coupled with its varied demography, unique dance forms and amazing boat stays .it has access to road ,rail and air too .air is most preffered .
*so overall ,if you want a holiday time without much exertion and great experience ,then kerela is on the list *I just checked online and found that there are some great packages available for kerela on tripoto itself. do check out this link
https://www.tripoto.com/kerela/tour-packages HAPPY TRAVELLINGdo