Recommended - Janome - (purps has 7025 John Lewis exclusive, and 9300DX overlocker, mini purps has a John Lewis own brand - made by janome)
Avoid new singer machines, they are not built like the old ones and I've heard lots of poor reviews of them.
Features I find helpful
Purps: Variable width and length, autobuttonhole and a good selection of stitches.
Twin needle capability for stretch hemming.
Adjustable stitch width and length.
Mine is a top loading bobbin, which makes it really easy to see when the bobbin is running low. It's really easy to load too, easier than the front bobbin on the mini's machine, but it's a nice thing as opposed to a really helpful thing.
Variable speed foot control, can use it in fast or slow mode, which is obviously something you can do by pressing harder, but the slow setting limits it so for tricky things you know it's not going to run away with you.
The ability to handle heavier fabrics.