TL;DR - EZ Drummer is your best bet. And get Logic X.
I find the drummer feature limiting tonally. Especially if I'm working on a progressive metal track. But, for me, I can coax a good "base" sound by doing the following (at least in Logic, I'm not sure how much of this actually applies to Garageband, and how much of it is in the same place):
1. Lay down a track you wish to be "followed" by the kick/snare. This is often the bassline, but might be the rhythm part. It should be choppy. You can always take an additional take playing nothing but palm muted notes or by playing staccato, and then mute it in the mix, if you're having problems with it "catching" your groove. Obviously, you should be playing to the metronome/click, otherwise it's just not gonna work.
2. Mess around with non-standard drums. The rock kit is your best bet (though not great) for anything metal/heavy rock, but try the funk kit/drummer out, for instance.
3. EQ everything. For simple EQing, hit "b" on your keyboard (at least within Logic, not sure about Garageband), and you can adjust the mix of each piece, compression, EQ, room mics, etc. Alternatively, if you right-click (control-click) a drummer region, you can go to Convert > Convert to MIDI Region, and you'll be able to modify it within the piano roll and hyper editor (again, this should be possible within Garageband but I'm not positive). Manual entry of MIDI data is tedious and time consuming, but you'll get exactly what you want. Use MIDI humanization to make it sound more real.
4. Want a fill? Create a new drummer region for a measure or so where you want a fill and max out the fill dial. Play around with the complex/simple and loud/quiet panel to find something that works within the context of the rest of the drum parts.
Unfortunately, there's no direct way to split up the individual pieces of the drummer plugin (even in Logic), so you gotta deal with what you have.
As far as external drum plugins, I've opted for Superior Drummer. I actually have spent the last couple months trying out every demo I can get my hands on. EZ is also really, really good, and one of the most inexpensive out there, but I wanted the added control and additional features. Tons of people use Toontrack's stuff, which is both a good thing and a bad thing.
The Good:
The best feature about EZ/Superior is that picking out pieces and building a song works REALLY well, and it's super simple to get a basic groove down without trying too hard. It makes songwriting within a DAW significantly less tedious. Bussing everything back out to Logic (via the multi-channel EZ/Superior option) makes it so you only really have to stay in EZ to pick your kit and a few loops (though I'm not sure if this is possible within Garageband). Everything else can be done within your DAW, and within the context of your own mix. Additionally, EZ/Superior are almost always on sale somewhere. I bought Superior for $179 off Amazon, it's normally $349 on their site (which has it reduced to $244 through the end of the year, which is still higher than Amazon, Guitar Center, etc.).
The Bad:
Sticking with the basic drumkit and loops results in you sounding like everyone else that uses EZ/Superior, which, in turn, makes it super easy to distinguish whether or not the artist chose to use EZ drummer or a real drummer for the mix. Simply changing some cymbals from their defaults and doing some manual EQing will help quite a bit. Another downside is the "crossgrade" from EZ to Superior (if you want to upgrade) costs just as much as a new license for Superior.
Based on what I've tried out:
BFD3 is perhaps the most expensive plugin out there, and, IMO, sounds the absolute best. It sounds the most realistic. However, it crashes like crazy and it doesn't give you the level of workflow you get within EZ/Superior. Plus, since it's not as popular as EZ/Superior, finding tutorials is harder, and added kits/bundles/whatever are more expensive than all the rest. The song generation and stability of EZ/Superior + BFD3's sounds would really be the ideal match (for me, at least), but I'm not made of money.
Steven Slate, in an A/B comparison, both with video demos and using the plugin, sounded like trash. The drums sound artificial. However, EZ has a bundle of Steven Slate drums available, so if you want the "Steven Slate" (drummer) sound, you can get it within an EZ bundle, and you've got the best of both worlds.
XLN's Addictive Drums sounded pretty good, but the interface was just... awkward, at least to me. It's also less featured than Superior, for not much less money (I think it was around $150 or so).
There are others out there, and others I tried out, but there's a reason Toontrack's stuff (EZ/Superior) are the most popular - both packages are easy to use, affordable, expandable, and sound great. There are a lot of albums out there that actually have drums written within EZ - Devin Townsend's Ziltoid the Omniscient is a prime example.
All that said though, I would highly, highly recommend picking up Logic X. The tools and features within Logic X greatly outweigh the tools in Garageband, it's just as fast to load up, the plugins are better, the samples are better, and, I believe, even the drummer is better.