SDR development has been somewhat incremental the past decade. The Perseus (2007) is still the SDR of choice for many DX-ers. Size hasn't changed significantly in this period. Neither has large signal handling, but there has been some development on maximum sampling rates, with the Elad FDM-S2 leading the way with a 6 MHz maximum bandwidth.
Now, things are about to change. Here are three possible record breakers:
Size: The Expert Electronics ColibriNANO is the size of a simple 8-bit dongle, yet has a 14-bit ADC like the Perseus, and can sample up to 3 MHz. Its frequency range is 0-55 MHz, up to 500 MHz with undersampling. As per the end of May, some preorder units have been delivered to customers, others (me) are still waiting. EUR 299.
Performance: The Airspy HF+ claims to be a paradigm shift in high performance HF radio design with superb signal rejection and stunning sensitivity claims (MDS of -138 dBm!). Frequency coverage is 0-31 MHz and 60-260 MHz. The architechture only permits a sampling rate of 660 kHz though. As per the end of May, the HF+ is not announced for sale. so we do not really know if it will happen during the summer. Price? TBA. I've seen mentions of a "target price" of < USD 200, but not from Airspy. Their current top model, the Airspy R2 + Spyverter (needed for performance below 24 MHz), costs EUR 289. My unqualified guess is EUR 299.
Capacity: The Elad FDM-S3 (sorry, I have no links to the actual SDR but I found the photo below on the internet) takes RF recording for the hobby market to an entirely new level with the possibility to sample 24 MHz! This will make FM DX-ers happy. I've read that it will cover 0-54 MHz and 76-108 MHz. As per the end of May no announcement of availability. It was shown on the Dayton Hamvention. Price TBA. My unqualified guess is EUR 899. The S2 sells for EUR 525.