I use it. It’s not the most intuitive app, but it’s the one I tend to use most, and the most “tweakable”. You’ll need mobile atlas creator to create any offline maps you need (which is pretty straightforward if you read the instructions). If you don’t, then it will try to use your 3g connection to download maps over the air – which will reduce your battery life or leave you lost somewhere with no signal.
Not tried MM tracker though.
Others I’ve still left on the phone are :
Maverick (paid) though there is a free version. Looks good and a simple UI, but it’s a pain to use.
Multimap
OS map