The functional component for an FPGA is the logic element which enables it to adapt to various hardware descriptions. This behavior is mostly due to the MUX-like functional flexibility provided by these logic elements or cells. However, in recent years, decelerating transistor sizing as per Moore's law has led to diminishing power, area and delay returns over cost. Hence, the idea of venturing into FPGA logic cell designs based on emerging technologies is becoming not merely attractive, but even inescapable. The present work surveys various conventional and non-conventional logic cell designs proposed in the literature by identifying four logic design families, namely LUT-based, cone-based, matrix/cluster-based and transistor array-based. We then carry out a detailed comparison at two levels - a quantitative comparison based on metrics like power, delay and area which govern the overall performance of various FPGA architectures and secondly a qualitative comparison on factors which are important considering the ease of mainstream adoption. We highlight the importance of introducing and co-optimizing novel devices and architectures to maximize the overall FPGA performance.