Of the Dells, I'll say I've had pretty good luck with a D630, E6220, and E7240 (current), all in pretty middling configurations (my current E7240 is an i3/4gb/128gb/1366x768) with very few complaints when judged against their peers.

I will say the E7240 was pricey given the specs (I want to say ~$1k from CDW right around initial release, purchased ~2 yrs ago) but it wasn't my money or my choice, so I'm just judging it on size/weight/durability/real-world performance. Right now it's not quite old enough to be cheap and not quite new enough to be a performance contender so I can't say I'd really recommend anyone seek it out, but it's a solid little machine for sure. My only real complaint is the docking station socket location makes it take up about 4" more desk space than is really necessary, but that's about it. At the time it felt pretty sleek but now it's almost pedestrian... there's notably thinner and marginally lighter available in 13.3" screens for around $600 most days of the week (mainly talking about the Asus UX305 series) and I've seen Amazon Warehouse Deals have them as low as $363. If I were shopping today, that's probably where my money would go.