Akos of the rtlsdr4everyone blog has recently written up a comparison of the RTL-SDR and SDRplay. The SDRplay is a $149 USD software defined radio with a 100 kHz to 2 GHz frequency range, a 12-bit ADC, and up to 8 MHz of bandwidth. It now competes heavily with the $99 Airspy Mini which is a similarly specced SDR.
Akos compares the two units and comes to the conclusion that the RTL-SDR is still the best choice for beginners, but that the SDRplay is definitely a good choice if you have good antennas in place and if the receiver is the major bottleneck in your setup.
In his review he goes over several points covering the costs involved, aesthetics, customer support, PC hardware requirements, setup, operation and finally reviews the performance of the SDRplay. His results show that the SDRplay generally receives much better than the RTL-SDR, but has some problems with broadcast FM imaging.
Also check out our own previous review which compared the SDRplay, Airspy and HackRF here.