As to entering old paper logs, I really haven't heard of any loggers that are superior to any others WRT that function. They all will require multiple mouse clicks and/or keystrokes to get EACH QSO into the log. Personally I use DX Lab's suite of apps and in the logging program, DX Keeper, and it can be tailored to optimize paper log entry but still it is somewhat labor intensive, especially if the data is not sequential, i.e. large deltas for time, freq, etc from one Q to the next will require a lot of manipulation of data fields.
Nice thing is once it is all entered into the computer logger, the time required work with the data to determine facts about the it is makes up for the data entry time in a hurry. Also managing the log becomes a simple task and you will actually find you probably have more DX counts than you thought.
When you're logging a QSO in "real time", your logging application should initialize the QSO's frequency and mode from your transceiver's current settings, set the QSO's start time to "now" when you indicate that the QSO has begun, and set the QSO's end time to "now" when you indicate that the QSO has ended, or when you record the QSO. When you're logging a QSO from a paper logbook, your logging application should initialize the QSO's frequency and mode from the frequency and mode of the last QSO entered from your paper logbook. This won't always be correct - as Gene points out above, you must manually enter the frequency or mode when either changes from the last-logged QSO -- but it does save a lot of keystrokes. When you're logging a QSO from a paper logbook, setting a QSO's start time to the end time of the previously-logged QSO will also require adjustment, but providing buttons or keystrokes that add hours, minutes, or seconds to start time can save time and keystrokes compared to requiring the user to type a full date and time for each QSO. These optimizations do let you fly through runs of QSOs made seconds apart on the same frequency and mode.
Not all logging applications can be configured to optimize for entering QSOs from a paper logbook.
There's a free application called Fast Log Entry
that is dedicated to logging QSOs from a paper logbook using techniques similar to those described above. It generates an ADIF file that you can import into most logging applications.