I would say perhaps a gelatin hydrogel. Depending on the net charge of your drug you could consider cationic or anionic gelatin, establishing electrostatic interactions and successfully entrapping the drug. We did this type of work recently using heparin as drug:
Article Crosslinked gelatin hydrogels as carriers for controlled hep...
Stimuli-responsive polymer particles, liposomes and mesoporous silica particles with smart gate-keeper are the potential candidate to deliver the hydrophilic drugs.
you can see our article:
Article Mesoporous magnetic silica particles modified with stimuli-r...
If you want to develop a nanopartcle (or) microparticle type of drug carrier, a cationic hydrophilic-co-hydrophobic block copolymer will work well. The cationic hydrophilic block will effectively load a hydrophilic drug which conatins any anionic moiety, while the hydrophobic block will be usefull for forming micelle structure.
If the drug contains any cationic moiety, anionic hydrophilic-co-hydrophobic block copolymer can be used as a drug carier.
By considering acidity (or) basicity of the drug molecule the copolymer should be designed.