WTF, that's not Ren Hoek in your avatar!
Seriously though, MAME looks like complete ass on an LCD monitor. If you read this board for a while, "monitor authenticity" is a big issue. The problem with CRT PC monitors is that the picture is too "good - it doesn't look like it did in the arcade. A genuine arcade monitor is the best looking / most authentic choice. A TV comes pretty darn close to an arcade monitor (some people will vehemently disagree with this, but some people agree). But to answer your original question, I've played MAME on an LCD monitor, and it was POO.
To answer your question about angle, it depends a lot on the height and distance of the monitor from you, as well as the overall shape of the cabinet. Some cabinets have a +/- 10-degree angle on the monitor, some are straight vertical, some (like Midway-style cabinets) have a 45-degree angle on them. If you're building from scratch, just see what looks and feels comfortable to ya.