In terms of accuracy and general capability, they are all much of a muchness.
All will record where you've been, with a similar amount of max capacity.
All the
Garmin 'leisure' or 'trail' models are also very well weatherproofed, and are generally recommendable. Other makes are either less weatherproof (Satmap, any smart phone) or generally less suitable for UK use (Magellan, Lowrance, both optimised for US use) and could generally be described as 'non-standard' in this context.
Knowing what I know now (4 1/2 years in) I would buy a Garmin
Etrex Vista HCx (the Legend is essentially the same thing) - with the caveat that this is now a fairly old model and Garmin are quite likely to market an updated version (pricier but not necessary better!) quite soon. So perhaps this is a good time to buy. However NB that the Etrex is primarily a walkers' GPS (although very popular with cyclists) and the cycle-specific ones are the 'Edge' range.
I would say in a nutshell, the Edge range has strengths in terms of being a beefed-up cyclecomputer, and in particular if you want to use it as a training aid (HRM, cadence, virtual cycling partner etc) - and it is undeniably prettier on the handlebars. The weakness is its sealed-in battery with limited runtime between recharges.
The Etrex range has strengths as a navigational aid (more capacity for multiple routes etc) and in particular is better for very long or multi-day (or even multi-week) trips because it has much better battery runtime and they are simple AAs anyway. The weakness is a general physical clunkiness and much obfuscation in the menus and setup department.
Two other Garmin types of interest - the 62 series which is their newest and probably 'best' model, similar functionality to the Etrex but a bit bigger - IMO too big and clunky for bike handlebars, better on recumbent or motorbike.
And their touchscreen models Oregon (larger) and Dakota (smaller) - these again have much the same functionality and are sleek on the handlebars, and can do HRM, and are generally simpler to operate - but I find the touchscreen is not a good idea on the bike, and also a bit dim to read.
To re-iterate, all these are walkers' models that can be handlebar-mounted (using Garmin accessory brackets) - of all the models, only the Edge range is cycle specific.
All the types mentioned can display a map (NB usually a hidden extra expense!) and at this stage of the game I simply wouldn't recommend a more basic non-map type (though they are completely capable in their own way).
Dont really know what i want but i think it needs to be able to tell me which way to go and record which way ive been.
Finally, I personally wouldn't expect any of these to be able to 'tell me which way to go' with any degree of reliability. In other words, as a cyclist I wouldn't put my trust in SatNav-type guidance, at least not on rural roads (its a bit different in a town). The way I use a GPS is to pre-program it with route instructions, which it then relays back to me at appropriate places on the road. It doesn't make
any decisions for me. The capability is there, but I wouldn't trust it and generally don't use it. Others differ on this - YMMV.