I think that it's high time people started thinking less about what they'll grab when, and more about what they'll have overall when they've all reached L10.
Furthermore, I think that anyone with skill enough to stop an initial skulk rush should choose their upgrades in a way that will leave the team better off once you're all at L10. This is a lot more important than being the first to grab a shotty to stop those rushing skulks (except for those one-minute games where the skulks just miraculously rush you and end it early on).
In some not-so-well thought out games I've had to start over at L0 just because as players joined the game and grew in rank, none of them thought that we might need a GL. When people reach the end of the game it is the better planned out team that will win (as evidenced by the team of nearly all super-skulks that may have owned early on, but can easily be destroyed later in the game).

For 10 people (What I believe is a nice number for clan matches), I think this is the best configuration, regardless of what you grab first, last, or in-between. If you're going to win at the end of the game, this is the best team to be left with. Because of its versatility it is able to cover or counter most of the Kharaa's strategies, although it should be adjusted depending on the opposing team. (If, say, there are 5 oni and no Lerks you may been a few more JPs w GLs!).


Heavies:
Armour 2, Heavy, L2 HMG, Welder
Armour 2, Heavy, L2 HMG, Welder
Armour 2, Heavy, Resupply, L2 GL
Armour 2, Heavy, Resupply, L3 Shotty -or- L2 GL/HMG

JPs:
Armour 2, JP, Resupply, L2 GL
Armour 2, JP, Resupply, L3 GL
Armour 2, JP, L3 HMG

Base Guard/Backup:
Armour 2, L3 GL, Welder, Mine
Armour 2, L2 HMG, Welder, Mine, Movement
Armour 2, L3 Shotty, Mine, Scanner, Resupply -or- switch to HMG


This setup allows for:

4 Heavies: Enough to take down an onos should one be gobbled up.
3 JPs: They can force 2 (or maybe more, if they can get their JP/weapons quickly enough?) of the enemy team to permagorge, and also quickly go back and forth to help out the heavies or base guards. They will also force a lot of the enemy team to Lerk, and if half of the enemy is either Gorge or Lerk, things are a lot safer for the Heavies.
4 GLs: enough to take down webs, or if the marines are beaten back into their base there are enough GLs to have both entrances covered with explosions (two per entrance, and as one reloads the other can fire).
4 HMGs, 2 Shotties: Enough to take down some oni or fades (especially with the GL support), and the shotties should take care of those pesky late-game super skulks who manage to run in circles through the heavy train (yes, we've all seen a skulk weave his way though, biting heavies, and all they seem to do in retalliation is shoot each other's feet).
4 Welders: It won't be easy for the Kharaa to take down the CC, or even the armoury. This is why the base defenders don't need resupply. Just make sure that when someone with a welder spawns they check the buildings before walking off!
3 Miners: By mid-game the marine base should be well strewn with mines, and the defenders can begin to litter the mines elsewhere in order to soften any approaching hoards.
1 Scanner: An early scanner sweep will be enough to keep most of the Kharaa from bothering to ever get this ability; it's more of a deterrant than anything else. Don't wait until half of the opposing team is cloaked before you get this upgrade.
1 Movement: There only needs to be one guy with this upgrade, feeding his team constant reports from the safety of the (mined) base.

A GL is Far more effective, especcially a baseguard, with motion. If you have another man with motion, yes it helps, but you can't aim. There I stick by the fact that every GL should have motion. That way you know what you're up against, and can use your weapon to the best of your ability, instead of having to guess when skulks will be upon you.

10v10 booo Clan matches are more like 6v6 and I hate 10v10 games. You have a good config, but this of course requires teamwork and wont happen. In a pub game if you have 2 onos and a lerk who keeps both in umbra its game over. Most lerks shoot umbra where the onos are at and not where they will be. To kill both onos it would take 3 level 3 hmgs unloading whole clip, so really you need even more than 3 hmgs because they will die before the clip is unloaded.

Ears are good, but MT is better. It's long-range, and spots silenced skulks.

Besides, most of us playing the game have headsets so we're only able to hear left-right. No surround sound for me It comes down to whether or not you want to spend the upgrade; personally I only like Motion for seeing when a whole group of enemies is trying to sneak around the group of marines, but for seeing where a lone skulk is hiding it's just not worth it. (Not to mention that once he hides he won't be running around so you won't be getting any more signals anyways.)

Oh, and I like 10v10 because it allows for two different good-sized groups to be at two places at once. In 6v6 you're usually stuck in groups of 3 or less, and things don't look good for you when your buddy gets gobbled up gobbled up right off the bat

2 groups of 3 moving in the 2 possible directions owns. I hate when 5+ guys are together half your bullets hit your own marines

correct me if i'm wrong, but you get only nine skill points and not ten (in your list you've used ten per marine:

lol, did I? I only remember that I wrote this sometime around 2:00 or 3:00 in the morning, after one particularly gruesome defeat. Come to think of it, I was counting to 10 the whole time....

-edit-
Yep, it says right there: 3:25! lol, I'll edit it....

the problem is that not the entire alien team is based on skulks
and knowing where your enemy is won't help too much for a GLer if it's a fade
extra fire power though, might

Forlorn, if you spam, you don't need to. But I aim, because it's more effective to use one or two 'nades on a skulk (depending on cara and/or 'nade level) than it is to use four. Not every grenade launcher has to be put to use madly shelling some useless corner of the map that nobody will run into anyway.

10 vs 10?
6 vs 6?

that just changes the total number of "lvl1 hmg, ha, welder, resupply-marines" from 6 to 10

I prefer 10v10 not because of umbra, but because to win a 6v6 game all the Kharaa have to do is have 3 Onos, 1 Fade, 1 Lerk, and 1 Gorge. That's half the TSA team gobbled up, and by the time they respawn they have 3 hungry onos facing them, shrouded in umbra, with a Fade killing the chair (or switching w the Onos so that they have time to heal while chair killing themselves) and a Gorge sticking webs all over. In 10v10 You tend to never get that many onos, you'll get 3 Onos at most, even when the plan is that half of the mwill onos, some of them won't follow through. In 6v6 it's better organized.