Best option is thailand for now. 2 days bangkok and 2 days phuket or krabi. or go fro bali. both have visa on arrival and no visa fees now. for bali you need to just submit a online permission form i think.
Best place is Thailand, but as you only have 4 days, try to plan your trip for only two places.
My personal favourites from Thailand are Krabi and Phuket.
Krabi is more peaceful place and you may relax at the beach while Phuket is very happening place and has beautiful nightlife.
Hope this may help.
You don't need visa to visit Nepal and it is a very beautiful country. You can also go to Thailand for 4 days to visit just Krabi and Phi Phi Island. Thailand government is providing free visa on arrival till 30th April for Indians. Please refer my post on my recent visit to Thailand under my profile where you will get an idea on what places you can visit.