First, for light aircraft, it doesn't really matter all that much.
While there have been lots of different styles of navigation computers, the experience of WWII cast most to the scrapheap with the two left standing being
(a) the Dalton, developed by Philip Dalton and used by the Allies, and
(b) the Dreieckrechner, developed by Siegfried Knemeyer, and used by the Axis. Somewhat later on, this machine was refined a lot by Ray Lahr at AA. Subsequently, the rights were sold to Jeppesen and the rest, as they say, is history.
Pros and Cons ?
The Dalton (the one with the slide) usually is of alloy construction and pretty much indestructible. The only problem is that most variants don't incorporate the scales to suit higher speed, higher altitude operations (ie where Mach Number gets to rear its head). Also, the device, physically, is large and it definitely won't fit into your shirt pocket. The wind triangle solution is probably marginally easier on the Dalton than the Jepp. For light aircraft GA ops, Dalton would be my choice.
The Jeppesen (the one without the slide and with the very misunderstood ETAS values) is usually of plastic construction so please don't put it up on the dash in summer otherwise you can plan on tossing it into the bin at the end of the flight and spending a bunch of dollars on a new one. These incorporate the higher Mach scales which make them useful for the high flyers. Also, not having a slide, the smaller unit fits nicely into your shirt pocket. For jets, I would go for this unless you prefer a Dalton with the higher Mach scales.
Overall, the main difficulty is that they require some level of practice otherwise you will forget how to use them. This is a MAJOR problem in the present era of electronic units, FMS boxes and so on.
You must have one for the exams. You can either get the Jepp at the start or the Dalton for the RPL/PPL/CPL and then swap to the Jepp for ATPL.
That's about the size of things. Both will do almost all your requirements other than for (most of) the Dalton units without the higher speed scales which fall down a bit for the high flyers.
Which do I use ? Simple - I've got both and use both as the spirit moves me.
