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It really depends on your play style. If you're intent on rambo-ing, (common noob tendency) nothing will really save you, but someone with a lot of health, or an easy escape ability (windwalk, etc) will probably help.
If you're more cautious, someone with range and reasonable movement speed can give you a bit more time to react, and running away a bunch of times can help you get a better feel for the map.
Trying a bunch of heroes is fun, but I'd recommend narrowing it to one or two until you get a hang of items, etc. It'll be less frustrating in the early stages, and you can still learn about the other heroes' abilities by being observant and checking what items they're getting, while not having to learn about new skills every time you play.