All of the modern ‘outdoor’ Garmins are pretty similar in what they can do – eg Etrex 20/30, Dakota, Oregon, Montanta, GPSMAP62, GPSMAP78. It is mostly just a question of whether you want a touchscreen or buttons, plus the size and shape.
Of the ones you mention, the Oregon is a bit bigger, with a bigger screen. So you can see a larger area of the map, especially useful if using OS maps. Plus the on-screen buttons are bigger, so easier to use if fat-fingered or wearing gloves. Though I think its a bit big for on your handlebars.
Personally, I would go for the Etrex, I think buttons are easiest to use while riding. Yes, entering text can be a bit fiddly, but you usually don’t need to do that very often – I find its quicker just to do “find nearest”, and pick the place from the list.
If you’re not interested in heart rate / cadence, I would suggest the Etrex 20, it is a bit cheaper. Plus the Etrex has better battery life than the Dakota and Oregon.