Yes, i agree, never sell an engine! Especially XL engines, they are just to expensive. Atlas mastery pack is a decent buy, if you are liking the assaults. (sad part is the 340 is an engine that is very popular in atlas builds, though mine i think i run a 320, 330 and a 340 in the 3 i own.
Personally don't sell an engine till i have 3-4 stashed away, Or are engines under STD's under 240, as the mechs that i would run something that small i go with XL's. Some still will use an STD in mediums say like a 220 or something, but i find most of those builds far to nitch to worry about, and typically don't fit my style.
But as far as atlas's go, everyone has an opinion on every mech, and the top comp players typically find others, basically what ever the top OP mech is at the time and then will move on. Us normal folks find mechs we love and then play um to death,, and don't care what other people say about how much our favs suck.. (commando's i'm talking about you
![:P](http://static.mwomercs.com/forums//public/style_emoticons/default/tongue.png)
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Atlas's have tons of great builds, I like combos with ac-20, large lasers and SRM's for starters, but dual AC5's, gauss, pulse builds, medium pulse builds are all great.. I just recommend if you want to use LRM's you don't run more than one launcher, and typically it's a 15, though at times a pair of 10's is nice as well. Just remember even long range atlas's need to move up to the front lines to help soak damage, so don't be that guy hiding in the back lobbing LRM's from an atlas.. Use them as the long brawler style.. aka 250-400m. Much shorter arcs, and they are far more likely to hit.
just think, by the time you master your atlas's you might have enough for that third battle master, Or maybe by that time the hellbringer will be on sale
Enjoy!