If you have to have a new one, get a Miller 140... I love my 135 and have figured out how to make it punch up in class when needed...
A good tool makes learning easier. Welders are no exception...
But I'd be looking in Craigslist for a deal on a good used one if it was me. The reds and blues pretty much last forever and you could end up with something multi-process that you could grow into.
Also, like with any tool, once you start using it how you thought you would, you start realizing all the other stuff you could do with it "if it was just a little bigger/more powerful."
So by all means, buy a 140 from miller or lincoln if that's what you have to do. But it's always a good idea to get a more powerful unit than you think you'll use... WITHIN REASON... Like I don't think you need a welder the size of a Smart car just for your home shop... But if you could get into a 240v welder and not completely blow your budget, you'll probably be happier in the long run. And as soon as you start welding sheet metal with MIG, you're going to start wondering about TIG, so multi-process might be a good long term option even if you don't think you'll use it today.