Each angel has it's own personality. Some mature and are fine with even the smallest fish, then others mature and give the word aggressive new meaning. I've kept angels for over 30 years and currently have 12 mature adults in a 220g heavily planted tank with mostly all small fish. What I can tell you is over the years I've found if you get a young angel/angels and raise them with the fish you choose you are less likely to have issues when they mature as they are used to the fish they have always been with. IMO fish that work well with angels are Rummynose and Cardinal tetras, yo-yo loaches, cory cats, whiptail cats, otos, Threadfin Rainbowfish, Dwarf Neon Rainbowfish, Honey Gouramis, Dwarf Gouramis, sometimes Pearl Gouramis. Other tetras that have worked are glowlight tetras, black neon tetras, congo tetras, and sometimes emperior tetras. Cherry barb will usually be okay with angels. German Blue and Bolivian rams work great with angels. And lastly Rainbowfish can be kept with Angels.
All that being said a 30g isn't overly large so a good stocking would be something like 1 angel, 6 cory cats, a honey or dwarf gourami, a school of 6-8 cardinal or rummynose tetras, 1 or a pair of German Blue Rams or Bolivian Rams (GBR's need to be added about 6 months after the tank is set up as they don't do well in new set ups, but Bolivians are much hardier), and maybe a longfin albino bristlenose pleco.
