I’m building an ES sorceress and i don’t know what skill to used as the attack skill, it has to be a skill that is good enough without too many maxed out synergy skills, so i was thinking Forzen Orb? But i recently got to hell and found that it was kind of weak when you only max out frozen orb itself and none of it’s synergies. What do you think?
I already have Telekinesis and ES to max out so that leaves three other maxed out skills.
nova is pretty stronk.
if you want to play full ES you want to get Energy Shield to lvl 40. no need to max it. put your gear+inventory on, cast battle command from CTA or barb and spec so you have lvl 40 shield 
add 1 point wonders like warmth/static/frozen armor.
then you can decide which element you want to play but there are not many choices tho. pretty much fireball or nova.
for fireball you max FB/mastery + synergies
for nova you max static + nova + mastery.
Nova is waaay superior to any other build in game 
start with crescent moon runeword then swap it for self-wield infinity
worth mentioning that you shouldn’t care about your resistances. they don’t do much with ES build My nearly perfect nova sorcs res: 2/-70/2/72
What do you mean by getting it to level 40? with “+1 to skills” items to raise it’s level to 40?
yep you want lvl 40 with items + inventory + your hard points + battle command
depends on how you want to play. despite what is believed to be common knowledge, ES is not an all or nothing type of skill. it can be mixed and balanced to the rate that you like. so this comes down to the kind of character/playstyle you want.
if you want to be a full dedicated ES and avoid blood mana areas, nova is probably your best bet. nova is more mana dependent than others, and the more mana you have, the easier it is to regenerate that mana. its a good balance of short range aoe stun locks with the safety of ES and the mana recovery of being full energy.
do you need to be full energy for full ES? no, you dont. i wouldn’t build full ES and full vita, but you could easily go 20vita/80energy as full ES and perform well.
do you need to go full ES? no, you dont. you can go minimal ES (max telek but 1pt ES) and still be vita. you use your mana pool as a blanket dr%, but still have the tankiness of vita.
do you need to be fully vita for a minimal or partial ES? nope. you can blend and balance as you like. if you wanted to go 80% ES, you can go something like 40vita/60 to 20/80 stats and perform well. it just comes down to finding a balance relative to your active skill build and the items you have and the ES% you want
Play an enchant sorc with a demon machine. ES makes them invulnerable and they don’t use mana at all in combat. They absolutely own.
I would warn you against nova if you are budget. It requires a lot of +skills to reach decent nova damage after your ES hard points are allocated. And you need that damage for stunlock threshold. In Hell, you will find many areas immune. Other players will tell you to simply weild Infinity - one of the most expensive items in the game.
Youre better off with fireball and farming places like AT or meph. Once you have a lot of wealth, you can respec to nova. I say all this having very recentlybootstrapped a nova sorc in Hardcore. She shreds everything until late NM, where you hit a wall. That wall grows very large in Hell acts 2-5. Now that being said, she is basically invincible, and very fast. Clear speed for Arcane Sanc is unmatched. But were looking at 15 minute trav clear time per run, unless you wanna rock lightning sunder (which I dont recommend for budget either).
Overall my estimation on nova is it requires best in slot to be effective and farm quickly. And if you already have that - what do you need to farm for? Ber runes do not rain down. They cannot drop from countess which can be easily farmed by nova sorcs. However you can find them (I believe) in arcane sanc. If you have the dedication, this is where you can bootstrap ypur infinity. Be prepared for 3 hours a day for a month farming however.
This fireball build worked wonders for me. Because fireball has a smaller aoe compared to nova but does way more damage it is better for elite sniping or boss killing, also amazing for farming all of the keys. For gaining experience just go to whatever is the terrror zone and snipe the elites.
Fire sunder, anni, torch charms. and extra fire skillers are nice for one-shotting or two-shotting certain fire immunes.
Flickering flame, tal rasha orb and chest with fire facet. Tal rasha ammy, 35% fcr spirit, 2 SOJ, Arachnid belt, magefist gloves, sand trekks for poison resist if needed. 105fcr fireball build. Pump energy shield and telekineses until you feel comfortable withh the tankyness, rest in fireball , mastery, meteor, then firebolt is last skill if you need the extra synergy.