If its the one I saw in the carphone warehouse yesterday its the Garmini3 streetpilot, got mine 12 months ago for �159, great little satnav, still using it, but probably getting a bit dated now.
Don't know which is the most reliable but I bought a Medion P100 earlier this year and she's taken us over 10,000 miles without losing us. She does have a glitch though: occasionally she forgets to to tell us which direction to turn: she'll say something like "please in two hundred yards onto the A2" A quick reset resolves the problem and according to tech support, we're the only ones in the world suffering from the problem.
She's not particularly effective in cities - she's more of a country girl and tends to get confused and panicy in the middle of Edinburgh and Liverpool. So you'll need to use a bit of common sense and patience when using her.
The advantage is that she's petite and slim yet has an easily readable face. She's portable so can be used for walking and cycling. Cost me �200 but I think they're probably cheaper now.