There are several devices on the market:
The original USRP, a.k.a. USRP1
This is the one that has been used in the beginning, before the UHD driver replaced libusrp, and is still on the market today because it's the only usrp that supports two daughterboards. While it's been used a lot, it's lack of 1PPS and 10MHz reference clock inputs, and less flexible clock generation requiring resampling on the host makes it less attractive than it's successors. They connect to the host using USB 2.0.
USRP2 and USRP N2xx
The networked series connect to the PC using 1Gbps Ethernet, that allows wider bandwidths. They can be used successfully with ODR-DabMod through the UHD driver.
The successor of the USRP1. It is the cheapest USRP, and is probably the best choice for both experimentation and transmissions with the mmbTools. If you want to start, take the kit with the WBX daughterboard.
More recent development, that has partial support from ODR-DabMod. It lacks shielding. Host connection: USB 3.0.
Contains an embedded ARM processor that cannot be taken advantage of by the mmbTools. Call for volounteers: If you want to port ODR-DabMod to the USRP E100, doing the modulation on the ARM and the FPGA, please tell !
Daughterboards for USRP and Analog Parts
Find in this section some hardware experiment done with USRP RF front end like daughterboards or external devices (filters, power amplifiers).
The following Ettus daughterboards can be used for transmission in VHF band III:
- Example of RF amplifier for DAB for VHF band III (never connect to an antenna without a license !)
- RFX400 daughterboard modification to operate in VHF Band III (around 200MHz)
- WBX daughterboard wide band coverage
- DAB in L Band test with the WBX daughterboard
- Filter to kill harmonics
- Carrier Shaping Mask
- Antenna for digital radio broadcasting
While the USRP devices can be used for stable operation in many situations, it is sometimes tricky to find the right configuration and system settings to achieve good results. Here are some hints and remarks to increase reliability.
- Make sure you use released versions of UHD and GNURadio, and not just the latest git checkout
- Compile the mmbTools with the correct ./configure options
- Monitor for USRP Underruns 
- Disable all useless services on your machine
- Disable CPU frequency scaling
- Try different USB ports, or even USB controllers for bus-connected USRPs
- Try to change the num_send_frame=128,send_frame_size=1024 UHD options