I'll answer this with comments rather than direct answers unfortunately.
If you are not budget constrained and want this unit purely for the bike and primarily around town with some adventure riding then a Garmin Zumo is the way to go
https://buy.garmin.com/shop/shop.do?cID=135
I don't recommend car units due to water/dust proofing, powering, ease of button use issues.
If you want to do mainly adventure riding (and also tramping/walking) then you have more choices
https://buy.garmin.com/shop/shop.do?cID=145
The Garmin Montana and Oregon are touch screen which is good and bad. They tend to have bigger screens (good) but harder on batteries and not sure about screen durability with the dust and grit etc. The Montana 650 is a very nice unit - probably the pic of the Montana and Oregon bunch. I've already got topo's so I'd probably not go for the Montana 650t though topos are bloody nice to have.
GPSMap 6? series is seen as the premium hand held, more tramping orientated units. 62stc is the top of this line but you need to think about if you need the topos and the camera. Most I know go for the 62s which is just missing the topo's and the camera. Very nice unit, slightly bigger screen than the eTrex series, slightly worse battery life, easier to use given more buttons (less wading through menus). The GPSMap 7? Units are for boaties as they float. Apart from floating and buttons above screen they are the same as the 6?
eTrex series is the budget conscious version of the GPSMap 6? Units. Slightly smaller screen, longer battery life but the eTrex 30 has all the functions of the GPSMap 62s, just slightly harder to use with less buttons. The 10, 20, 30 are the new units and the Legend, Vista, Summit, Venture etc are the older models. A few years back the H version of the Legend, Vista etc was built with a high sensitivity receiver which actually made it better at keeping at satellite lock than the GPSMap models at time. The eTrex use to have a lower sensitivity receiver than the GPSMap hence was the budget version but this is no longer the case.
I've personally got a eTrex Legend Hcx which is pretty much the equivalent of the eTrex 20 except for a couple of extra software features on the newer 20. I'd personally go for a 62s if budget was not an issue or I'd the eTrex 30 if budget was an issue. If budget is a really big issue the cheapest unit I'd get is the eTrex 20. Only reason I'd not go for a 62 with an s or a t is that I'd not bother with a camera or the topo maps as I don't need them.
Sorry the answer is not more straight forward but hope this helps.
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