Should I go for an oil based or water based paint?
I used oil, mostly because I'm oldschool. Lots of thin coats
Any particular brand you guys would recommend?
Try Zinsser B-I-N Primer/Sealer, some would argue the best primer out there. It does a good job of sealing the MDF, as it can 'offgas' for sometime. The paint was just a high-gloss interior alkyd paint. Don't cheap out on quality
How to go about to get a nice clean glossy looking finish?
Lots of sanding, lots of coats of paint. Two coats of primer, sand, paint. Keep sanding between coats, going from a rougher grit to a smoother grit as you go along. I can't say how many coats I did on my cabinet (gloss black by the way), but it came out looking great. By far the longest process of the cabinet build. Just take your time. I also used a foam roller, as it gave me the smoothest coats each time. Read the post above, it's got lots of great info in it.