From personal experience, I would definitely recommend one of the big workshop type trolley jacks, as opposed to the DIY smaller ones.
Reason: ease of use, build quality, sturdiness and they generally do a better job.
I borrowed my grandads massive low profile trolley jack (workshop style) to get under my Z4 to replace the handbrake cables and it done a fantastic job of lifting the car high enough for the rear wheels to sit on ramps.
In contrast, my cheap small one just about lifts the car high enough to remove the wheels. It's good for the simple things, but for bigger jobs where you need axle stands to get under the car, the bigger industrial types do a much better job.
The Arcan trolley jack posted on the previous page is very highly recommended in the car enthusiast community, and comes in at under £90! Bargain. It's definitely low profile.
http://www.costco.co.uk/view/p/arcan-2000kg-aluminiumsteel-service-jack-model-hj2000eu-900930