These two garlic presses seem to be the most popular on Amazon right now, and since I've used both, here's my two cents.
OXO: this is a much easier press to use, requiring far less hand strength. It's also the easiest to clean (just flip it backwards and the red plastic head cleans itself). Mine has done just fine in the dishwasher top rack. However, it can't handle unpeeled cloves, and does have a tendency to break at the hinge every 2 years or so (I used it almost every night). It also leaves slightly more unused garlic residue inside.
Zyliss Susi Deluxe: I bought this after breaking my third OXO. It requires substantially more hand strength to use. It can press unpeeled cloves, but you have to squeeze quite hard to do this. It is slightly harder to clean than the OXO (use an included attachment), but still much easier than other garlic presses. This one leaves practically no unused garlic residue inside. I've only had it 4 months, so I can't comment on durability yet.
Overall, I'd get the OXO if you have arthritis or if your hands aren't strong, or if ease of use and cleaning are very important to you; just plan on replacing it every couple of years if you use garlic every night. I'd get the Zyliss if you have strong hands and don't want to peel the garlic cloves, or if the breakage rate (or leaving behind a tiny quantity of garlic) bothers you. I'll probably stick with the Zyliss, but I'd buy my mom the OXO (and replacements).