IME the 5 worst African cichlid community residents I've had:
1 - Neolamprologus christyi - By far the most aggressive african and easily the most aggressive cichlid I've ever kept. Big (by Tanganyikan neolamprologine standards) mean fish (to 8.5"), a pair should have at least a 55g to themselves, if you want tankmates with an adult pair, I wouldn't try it in anything less than a 180. A lone male *might* work with tankmates in a tank with a 60" x 18" floorprint or larger.
2 - Telmatochromis dhonti - A very aggressive Lamprologine type cichlid. They have a really bad reputation among aquarists and while they're very aggressive, it's slightly overexaggerated IME. They're still a few steps down from N. christyi in terms of outright aggression. They don't get too big (~5") and in tanks upwards of 90g a pair will do fine in communities if they're given a well defined territory and tankmates are carefully selected and grown up with them. A pair would be comfortable in a 30g, but they'd have to be kept alone.
3 - Melanochromis melanopterus/chipokae - The larger Melanochromines (5-7.5") with elongated snouts. Opportunistic predators and very quarrelsome. They're just like any other aggressive mbuna; relentless bullies. If they decide they don't like another fish, they'll constantly pick at it. They're doable in community situations with other tough fish in tanks above 75-90g, but make sure you actually crowd the tank to disperse the aggression so it's harder for them to single out a fish to pick on.
4 - Melanochromis auratus - Melanochromis auratus is every bit as aggressive for its size as M. chipokae but stays quite a bit smaller (to 4.5") and as such might be a little more successful working in reasonable sized crowded communities (75g+).5 - Hemichromis fasciatus - The largest specie of jewel cichlid (to 9"+). Very, very tough fish, they can hold their own against just about any other similarly sized cichlid. I've found them to be variable in temperment; some are more passive and do well in community situations as long as others stay out of their way, and others are downright monsters.
5 - Hemichromis fasciatus - The largest specie of jewel cichlid (to 9"+). Very, very tough fish, they can hold their own against just about any other similarly sized cichlid. I've found them to be variable in temperment; some are more passive and do well in community situations as long as others stay out of their way, and others are downright monsters.
Lobochilotes labiatus is another big bruiser from Lake Tanganyika. Basically the Old World equivalent of Amphilophus labiatus but slightly larger and apparently more aggressive. My experience with this fish is very limited, so I didn't add this fish to the list. Same with Tilapia buttikofferi, from what I've heard about this fish I actually would probably place it in 5th place above H. fasciatus, but again, a lack of experience (I've only kept a few small ones, largest I've had died at ~8") caused me to omit it from the list.
Honestly, I'd avoid any of the above mentioned fish in a 30g (except maybe a lone pair of T. dhonti or a small, carefully monitored colony of Melanochromis auratus with some fast swimming target fish) and definately no tankmates that aren't disposable. Most of them get too big for a 30g and would require at least a 55g.