I don't have a preference for who I work with.
ISO 639-3: see
Seneca is a language spoken in upstate New York on the Allegheny, Cattaraugus, and Tonawanda reservations. Currently ethnologue classifies the language as 8a, Moribund, and there are <100 speakers remaining. It is considered to be a poly-synthetic agglutinative, and has a rich inflectional morphology system that uses both prefixation and suffixation.
There is an active revitalization effort, so many sources are available online.
ISO 639-3: lkt
Lakota is a language spoken primarily in North and South Dakota. Currently enthnologue classifies the language as 8a, Moribund, and there are ~2100 speakers. Lakota is an agglutinative language with inflectional morphology. The language uses mostly prefixation but there is also some infixation.
- Online corpora 
ISO 639-3 tiw
Tiwi is a language spoken in Bathurst and Melville islands in Australia. It is classified by ethnologue as 5* developing, and there are 2,040 speakers according to the 2016 census. Traditional Tiwi is highly polysynthetic, but modern Tiwi is isolating language with some inflectional morphology. The exact number of speakers of traditional Tiwi is unknown.
- Language texts