Aldi are retailers. You'll get it cheap. (Like Time?) If it works, it will be fine. If it don't, do they know how to fix it?
If you are going down the local superstore road, go PCWorld. Advent or HP. Do you need a new monitor? PC World will sell the computer without one. You'll save buckets
Mesh build good computers at first class prices. But if you have a problem, you'll see from threads here that their service can be a little, well, frustrating. Call their help line before you buy to see if things are now running ok
Dell ship over a hundred thousand computers a week, many to businesses in quantities of hundreds. They can't afford to have them go wrong and, basically, apart from the rare hiccup, they don't. They are also extremely price competitive. I've just bought 2 5150 base units at around £300 each and haggled free delivery and one or two other bits of add ons. They arrived in 3 days and both worked out of the box
Consider what you want to use the computer for. Prices are low just now. Everyone is on the Costas and the base units are still pouring off the end of the production line. Haggle. And then haggle again!