I purchased a Garmin recently, and I hae also used a TomTom. Both of them were the cheap ones.
FYI, right now if you go to Dealnews.com you can get a TomTom 4.3" widescreen GPS for under 100 bucks.
OK, so they both get me where I need to go. Supopsedly, the Garmin has a larger POI database. It’s never foolproof, as some very common places that have been near my house for yeas and years are no in their POI. (Costco anyone? It has the one 10 miles away but not 5 miles away). The TomTom did a very nice job with directions as well, and if you have the address, it’s pretty moot.
The TomTom does tend to be smoother in my opinion, where the Garmin tends to move in a more tick-tick-tick fashion. And you can customize the lower end TomToms (different voices, etc) more than you can with the Garmins.
ETA: I purchased the Garmin based on its reputaion, before I had tried the TomTom. Knowing what I know now, I would probably lean toward the TomTom. Garmin supposedly has a better battery life, though (5 hours compared to 2 hours)