I've used L-Theanine, I found the first time I tried there were good effects but afterwords it died down a little, it sort of makes you feel "centred" 100% worth a try though, but I'm not so good at explaining effects of supplements. It works on the GABA and Dopamine system if that gives you a better understanding of it.
L-Theanine comes from matcha green tea, so I've tried various matchas to see what sort of effects they give you, so most of the Matcha teas I've boughten have done nothing, except for one time I went to a local tea shop (not a chain) and they had super high quality matcha and I had a large one and the effects were incredible. The effects were very different then just having theanine on its own, but it was an awesome an powerful feeling. But no other matchas have done that for me, so eventually I will go back to that tea shop and try it again, if it does the same thing I'm going to ask them for their source.
I've never used 5HTP but I have used tryptophan (very similar, it is a precursor to 5HTP) and it did nothing, I'm not sure i have the link but there was a review of studies on 5HTP and tryptophan and the results were always ambiguous they couldn't confirm it really did anything