In this paper, we examine the design trade-offs of several Watt-level 2-stage single-ended and differential Class-E SiGe power amplifiers (PAs) at 2.4GHz. The circuits are designed in a 0.35μm IBM 5PAe SiGe BiCMOS technology with through-wafer-via (TWV) technology to minimize the detrimental parasitic ground inductance. SPICE simulations show that a 2-stage single-ended cascode PA can achieve high power gain of 30 dB with output power Psat/P 1dB =29.5/27dBm, peak power-added efficiency (PAE) of 51%, with -30dBc 2nd order harmonics and -44dBc 3rd order harmonics for CW input. Using a low-loss output balun, a differential PA can deliver higher output power than its single-ended counterpart; however, our proposed TWV-aided single-ended PA exhibits much better PAE with a smaller die area than its differential PA counterpart. The advantage of the differential PA will diminish quickly when the loss of the required output balun reaches above 1dB.