Since 2.1 dropped, doing missions and hopping into signal sources has been most of my game time. I pick up more missions pretty much on every stop, using the supercruise transit to drop into USSs.
I have used 3 ships for that:
1 - Cobra Mk3. One of my favorite ships, I use 2 medium railguns and 2 small missile launchers, class 4 shield shield and milirary hull. Great for missions and signal sources, fun to fight in it, agile enough for make it easy to use railguns, very versatile ship. In the odd case things go south, its very easy to bolt. Its main drawback is its lack of cargo space. Can't pickup that many missions, worse when you carry limpets. That's why after a while I started using the:
2 - Asp Explorer. A lot more space for limpets than the Cobra mk3, allows for a lot of limpets and spare cargo space. Also allows to pick up more missions. I use it as a full missile boat, lays waste to NPCs on those USS and pirates trying to nab my modular terminals.
3 - Python. I sure as heck don't enjoy flying it nowhere as near as the Cobra3 (or even the AspE), but the Python gets the job done. Well done. Any job. You can carry a buttload of limpets and will have no problem picking up missions. I use a large beam on the belly, and 4 multicannons on top. NPCs never know what hit them. Unfortunately, the Python is a soulless ship, so I usually get back to the Cobra3 after a while a the cycle repeats!
Fun factor: Cobra3 > AspE > Python, but efficiency factor Cobra < AspE < Python.
Go with Cobra!