I don't think you can go wrong with any of the manufactures still in production, and if you will consider buying used, there are others that may be just as good.
In a broad sense, youy wallet may determine which cars you look at as much as any sense of originality. Prices can range quite a bit, depending on how the car is finished off. Nowadays, you may or may not save any money buying an unfinished/kit car versus a "lightly used" one. Below is a rough summary of what you can expect to pay for a finished car. Of course this is my observation, and others will certainly have their own (probably more accurate) opinions.
Typically, space-frame cars go for a little less (lets say $55K to $75K or maybe $85K), and mono cars a little more (say $70K to the sky's the limit..what's HM asking for their Mark IIs...half million?). Gelscoe (UK) is several hundred thousand dollars, while SPFs run $85K to $150K (though I haven't actually seen one sell for $150K, there is a completed car being advertised for that right now).
Like everyone else, I'm hesitant to say which is best. Aside from originality, the ability to get FIA papers is considered an advantage by some, and this can be had with any of the upper end cars if built to spec (ie SPF, Gelscoe, Holman-Moody). CAV makes a very nice mono, but I'm not aware that they can get "papers". There are also several other very nice, but very low volume mono builders (GOX, etc). But these are only rarely available, and I'd guess priced in the SPF range +/-.
So there's my take on the market. Had you been looking 3 years ago, you could have really picked up some bargins. While they still exist, they are becoming few and far between.
If you're a "Dan Gureny"-sized individual, try to sit in some cars, it may narrow your focus. If you're "Jacy Ickx"-sized, you'll fit just fine in any of them.
That's my take. The humt is half the fun.