A cause of high ERP failure rate is the misfit between organization processes and ERP systems. To solve the misfit problem, literature suggests two adaptation approaches: conducting business process reengineering (BPR) to fit organization processes into ERP systems, or customizing ERP systems to fit organizational processes. However, extant studies seldom explore how firms should choose between the two adaptation approaches and adjustment level based on their heterogeneous firm characteristics. Through the lens of contingency based task-technology-fit (TTF) theory, this study collects data from 150 U.S. manufacturing firms that use ERP systems, and empirically investigates how firms could choose a suitable adaptation approach between BPR and system customization while considering their heterogeneous characteristics, such as firm size, industry, top management involvement, big-bang or phase-in implementation speed. Consequently, this study further examines how such choice of different adaptation strategies and adaptation level affect firms' final firm performance. Our results show that industry, top management involvement, and implementation speed significantly affect firms' choice of adaptation approaches and adaptation level, while their choices also significantly affect final firm performance.