I had a small tracker for a while and after faffing with it for a while sold it on eBay. So I may not be the best person to answer. But here goes.
You need to decide on the basic parameters:
what is the longest ride you want to log? (distance)
how long will that take? (time)
how often do you need to log? (I find that every 10m is necessary in urban areas because there are often a lot of route choices, 100m is fine for offroad and every few kilometres is ok for touring).
That tells you how much battery life you need and how many data points you have to store. I'd expect that the data points answer will be less than 10k. Battery life is what mattered to me in the end - I was uploading every few days and recharging when I did it. What ended up killing the idea for me was the lack of display on the thing. I wanted to be able to see how much battery life and memory it had left without plugging it into a computer. It couldn't do that.
edit: for single-day use note that there are only 80k seconds in a day, and most small loggers need a second or so to take a reading. So a 30k point GPS could log every single second you were on your bike each day. More reasonably, logging every 10 seconds means at most 8600 points in 24 hours. So a 10k point logger will be fine.
I think more important points will be GPS reliability, robustness and how waterproof it is. If you have to tape an antenna to the top of your helmet to get reliable reception that will suck, and likewise if it stops working because you went over a bump or through a creek. So I suggest looking at those features rather than focussing on battery life or data points. Work out where you want to mount it and run from there (in a backpack is quite different from in a pannier or handlebar bar, and different again from under the seat or on the handlebars.