I think I may have to try and get one or two people to help me talk / think out winners for this because its hard to pick - but after weighing some options and looking over the builds here are the results!
Winner - Kontraxe
Out of all the stock builds I like this one the best mainly for how long it can continue to use the AC-20. The 6 tons of AC20 ammo is what really won me over on this build - even though its not fast with a STD 235 (76.1 / 83.8 ) it moves faster then my hunchback-4SP which is still able to brawl really well and keep up to the assaults / heavies, but it will get juked by Jenners and fast lights. Recommendations: To counter this maybe drop a ton or 2 of AC20 and bump the engine up to the next level, you should still have enough AC20 rounds at 4 tons to last in a drawn out fight.
2nd - Deadfire
I like the idea of having the faster engine, but the problem is that it came at the cost of only having 21 shots. I know the AC20 is not the fastest thing to shoot but if the fight ends up going a long time you will have to drop down to the lasers really quickly. Recommendations: I think if the engine was bumped down one ton worth to fit one more ton of AC20 rounds then this would be a very good build.
3rd - Omigir
I really like the idea of the 2 UAC/5's but the problem is that the low ammo count won't let it be very effective in the field for long and as such you will be forced to just the lasers really quickly. Tried to remove the MPulse but due to no more crit slots left you can't add more ammo and just have 2 normal Mediums. Good attempt, I like it a lot.
Hope everyone had a good time! The next build challenge begins soon - next mech: 3C Trebuchet