I am not so adventurous in trying out the different plants as I find that not many plants are hardy and some are hard to maintain or may require soil, much light, fertilizer and CO2.
My favourite plants are plants that are easy to grow:
In my opinion, this plant has the most beautiful leaves or foliage.
It is very beautiful to behold.
But they are not as easy to keep as my other favourite plants as it requires brighter light.
This is also a beautiful plant, it grows very fast, useful to absorb ammonia and very easy to care.
I like this plant as it can create a refuge for shrimplets and is easy to care.
It could be also due to the lack of water agitation/aeration as you don't have filter in the tank.
The bad gases is building up in your tank.
Some plants may also die without water aeration, thus creating the rotten smell.
If possible, try to have at least an air stone in your tank.