I have tried most of the serp trackers that have free trials.
My favorite for just google is serpfox. Most of the time I have 2-3 different serp rankings on the graphical charts for a given day where as most just put a single rank per day. Also i've seen it pick up rankings to like 347...im not sure how far it checks for ranks but I like to know how far I drop instead of just a gap showing. I like the reports it generates..they don't look quite as nice as serpbooks and I don't see a white label option. Excel reports do show the ranking url.
My second favorite is serpbook because its got yahoo, bing, and backlink count in a convenient interface. Also generates nice looking white label reports...kind of wish I could have the ranking url in the pdf report...not really sure why serp trackers dont do that. Excel reports do show the ranking url. Serpbox stays in second place because of the gaps in my charts...believe it doesnt show up at all if its not in the top 250?
I havent tried serpbuddy yet as they don't offer a free trial and didn't even respond to me when I inquired about one.