If you're on a limited budget, then it would make sense to stick with the same brand, then at least you'll know your feet, bobbins etc will fit (although I think Janome/Brother may be interchangeable).
You say your current machine is running fine, so I'm assuming there's some reason - more features perhaps - why you want a new machine. I made a list of the features I really wanted, followed by those I'd quite like before I purchased my second machine (three machines ago, lol).
The important thing is to buy the machine that will make you happy - budget and features. If you want more of the latter, then you may have to save some more. Good luck!