If you want a top beetle go and check out the one Rodz got for sale

what are you after?

Daily driver?
Weekend cruiser?
old skool kool?

If you are after a reliable daily driver I would get a stock late model - 1600, disc brakes, 12 Volts, seat belts etc etc

Late models are not as "collectible" as early models (say pre 1967)
That means you get more bang for your buck in buying one

this is an example of what I am talking about
http://forums.aussieveedubbers.com/viewtopic.php?tid=101868 

What it lacks in "cool" it makes up in spades in value and reliability.

as far as a reliable motor, all of the stock motors are reliable if they are well maintained and driven as they are supposed to be. I would avoid a modified motor, they can be as reliable as stock but not all of them are...

you need to remember that any beetle is now an old car so will need more maintenance than a boring modern thing. i'd thoroughly recommend leaning to do the basic maintenance yourself. it is easy, anyone can learn if they want to learn. + it's really satisfying (and lot cheaper/easier than finding a good vw friendly mechanic).
i'm assuming from your user name you are female and therefore might have one of the cliché aversions to working on cars... if so name it and we will either work a way around it or put a spin on it so it doesn't matter.
if you do consider working on your car i'd recommend picking up a cheap copy (ebay) of "How to Keep Your Volkswagen Alive: A Manual of Step by Step Procedures for the Compleat Idiot" by john muir. (also known as the idiots guide). it is a great introduction to working on vw's and cars in general.

as for what is the best beetle for you, as said above, that all depends on what you want it for, how you intend to use it and also where you live.
if I lived in a major city and could only ever own 1 stock beetle that I had to drive and maintain for the rest of my life i'd choose a 68-70 1500cc beetle. cheaper parts, better electricals, more refined suspension, better brakes and reasonable power in a car that still retains some of the classic looks. thankfully those conditions don't apply so I have 50's and early 60's beetles.

it is generally best to buy the best car you can afford, but of course the most expensive isn't always the best. there are heaps of good people in the vw community so if you can find and befriend someone locally an experienced set of eyes can help you to differentiate between the cars that just look good and the ones that are good.

keep up your research, the more you know the better informed your decision will be.

If you at looking a beetle that happens to be modified make certain that it comes with the engineering approvals for them, some things are not legal such as narrowed beams and will affect your insurance and if involved in a accident could cause conciderable issues.