IMHO splitters are pretty generic, and there isn't a huge amount of difference in quality among the different brands. I have a Harbor Freight that has been good to me, others have been happy with TSC Speeco's, MTD's in their different brands and so forth...
One can get wars about engine brands and so forth, but it really doesn't make a huge difference...
I would look for a 20-ton or thereabouts, with a 5-6hp engine, 11gpm pump, and 4" cylinder, that can be used in either horizontal or vertical mode. Don't worry about brand all that much. This is the basic 'generic' splitter configuration, which will have an approximately 15 second cycle time and handle 99% of anything one might throw at it... To get fancier than those specs will cost significantly more in most cases.
Store or online doesn't matter all that much, but if going online, watch for freight and delivery charges - splitters are HEAVY and BIG, so you will be looking at truck freight, not UPS, which can get expensive really quick unless the vendor has some sort of deal... Some stores have free "ship to store" deals. HF has a flat fee charge for truck items, so this might or might not be an issue, but watch out for it.
Gooserider