I'm firmly in the "touchscreens are evil" camp, so prefer the eTrex over the Dakota for that reason. Otherwise, I don't think they're a lot in it, the software's basically the same.
But I'll query whether auto routing is actually faster: Ostensibly it'll give you a route from A to B via C, D and E by simply defining those route points. In practice, it'll probably give you a route that you don't want to cycle (it doesn't know about hills, or your preferences regarding main roads and sustrans paths), so you'll have to take time to persuade it to take the route you do want by adding extra route points (the best approach is in the *middle* of roads you want to travel along, rather than at junctions) until the algorithm's weighting is defeated.
Which would be fine if Mapsource/Basecamp used the same algorithm for finding a route that the unit does. It doesn't. So there may be inconsistencies that you'll have to check for, which is tedious.
You also have to fudge things when you do something that the map doesn't allow - typically a contraflow cycle lane, or the "ride to the end of a dead-end minor road, walk the bike across the scary dual carriageway, resume riding on another dead-end minor road" manoeuvre. My approach is to stick a waypoint there to tell you that's what you're doing, and ignore the incessant beeping and re-routing until you're on the other side.
Which isn't to say that auto-routing doesn't have advantages. Get this right and you get lovely clear turn instructions, and automagic re-routing if you get lost. But I'm not sure it's any faster to create routes.
