For the garmin legent/summit/vista get the H model, it has the newest extra sensitive chipset. 24M isn't a lot of memory for maps so I'd personally get one with the x. I have a Legend HCx and a 2G MicroSD card in it. I bought Garmin's City Navigator and was able to load the 48 states then all the topo maps east of the Mississippi with space for lots of log files left over. I set it to always log and store the logs on the card so I can have them default to .gpx files and not be limited, they truncate the logs on the internal memory to a certain number of points.
I load it up with a pair of Sanyo Eneloop AA's and have used it on and off for several days without needing to swap batteries.
Bought the bike mount most recently