When starting new game, first 2 or 3 warriors go exploring and attacking animals to get to 5 ,I usually pick woodsman 1 + 2. Is this a good statagy as I usually play at prince and under.

Sure woodsman 2 let you explore far and wide. Other option is combat 1 then medic 1 so you have a weak medic unit to go with any war stack for later(that way it won't get killed). Of course at prince you can warrior rush so the CR line is fully viable if you have any nearby neighbors that doesn't start with hunting...

I usually use combat 1+ medic for scouts, and woodsman I and 2 for warriors.
It's map dependent obviously, since some maps have more hills than forests.

Somehow, it's also strategy dependent.
For instance, if you're not researching military techs (BW or HA) early, you may need your warriors to be able to withstand combat vs barb archers.
Cover is then more valuable than other promotions.

I tend to go Combat I, Medic, March (if I'm lucky) for Scouts. I hate giving them the promotions they'd get for free when upgraded to explorer.

For warriors I go Combat I, Shock or Cover or CR I and II on the theory that they can form part of my axe-rush army when I get BW.

Upgrading units is way to expensive for such early units and hence planing for that is a huge waste in most cases. Not to mention that explorers are totaly useless on all non-terra maps...

My early warriors allways go the Woodsman line. Good for Exploring, Good for Worker Snagging, Good for perspective Medics.

My only scout, if i happen to have one, usually goes into the stomach of a Bear...

The upgrade costs do not matter much here. Most people do not upgrade the Medic unit anyway, to prevent it from dying on defence. While upgrading the Warlord-Super-Medic is for free...

Upgrading units is way to expensive for such early units and hence planing for that is a huge waste in most cases.

I wouldn't agree. Late game you can produce new units, probably with at least a couple of promotions in a couple of turns. At that stage of the game its only worth upgrading elite units. For an early axe rush speed is important and 1-2 extra axemen with 1 more promotion than your barracks can produce could make the difference.

Not to mention that explorers are totaly useless on all non-terra maps...

1 of those generalisations that is wrong in many cases. Map type, number of AIs, barbarian setting - all these can make Explorers useful.

Straight Combat Line is the safest way to go, especially with Animals where things like shock and cover won't help. I get caught too often with my woodsmen warriors wandering through a glade and getting attacked, and hills don't seem to be common enough on most maps for merriting that line.

Upgrading units is way to expensive for such early units and hence planing for that is a huge waste in most cases. Not to mention that explorers are totaly useless on all non-terra maps...

The cost is indeed high to upgrade, but saying explorers are useless is simply a stupid thing to say.
Explorers make superb healers in offensive stack :)

Generally, unless I have about twice as many forests as hills, I prefer Guerilla (sp?) to Woodsman, for the simple reason that you see farther if you're up on a hill.