Hello,
to start with Brahms, I can say that
Rhapsody Op.79 No.2 in G Minor is a good choice because it's dark, strong, dramatic and impressive. Here it is Martha Argerich's famous recording:
His
Ballade Op.10 No.1 in G Minor is also beautiful. Michelangeli plays it:
Intermezzo Op.76 No.7 in A Minor. Kempff:
Intermezzo Op.119 No.1 in B Minor: Richter!:
Dark and haunting,
Intermezzo Op.118 No.6 played by Richter:
Also,
Waltz Op.39 No.4 in E Minor (it's very short and much easier than all the above, but pretty and romantic!). Kissin (the last piece in the video):
Intermezzo Op.117 No.3 in C sharp minor played by Kempff:
Brahms has transcribed his first
10 Hungarian Dances for solo piano. But they are technically difficult pieces. For example:
As for Schumann,... hmmm...
Albumblätter Op.124 No.1 - Impromptu:
Of course
Kinderszenen Op.15:
And
Kreisleriana Op.16:
Fantasiestücke - In der Nacht Op.12 No.5 in F Minor:
Fantasiestücke - Aufschwung Op.12 No.2 in B flat Minor:
Romance Op.28 No.1 in B flat Minor:
Just a question, why do you want this romantic piece??? For a concert, your lesson or just for yourself? If I knew, then maybe I could think about something more specific and suitable for a concert or a lesson, for example. I'll write again in a few days, if I come up with more ideas!...

I hope I've been of some help to you!

Bye for now and GOOD LUCK,
Evitaevita.