The TI-83 is historically regarded as one of the best calculators, but the TI-84+ is recommended for its enhanced features and usability. The TI-89 offers advanced capabilities but is not permitted for the ACT test. The TI-83/84 series is user-friendly and suitable for business and technology majors, particularly due to its strong statistics functions. For those heavily involved in statistics, the TI-83/84 may be the top choice. The TI-89, HP Prime, and HP 50G are suggested for more advanced users, while the TI-Nspire is noted as a potential math tool rather than a primary calculator. For pocket calculators, options like the HP 35s, TI-36 Plus, Casio fx115 ES, and HP 17Bii are highlighted for their unique features. The HP 48 is mentioned as a favorite among engineers, but since it is discontinued, the HP 50G is recommended as a modern alternative.