I absolutely agree with everyone who recommends an older machine and a good service centre. But I've gone against that advice for myself and have a newer computerised machine for myself, simply because it has a needle threader and my eyesight is not great these days - I was starting to struggle to thread the needle on the older machine.
Anything that's not the cheapest machine will generally be ok. Most of the fancy options that make machines expensive are not really necessary, as long as the machine can sew straight and zig-zag you have nearly everything covered.