Re: Max synergy vengeance viable?
Maxing Holy Shield is not at all necessary. Diminishing returns become noticeable around 5 points, and past 10 points you get very little. To illustrate, the first five points give you +25% block, the next give you an additional 5, and the next ten also give you only another 5. So, with slvl 20 HS, you get +35% blocking. I'd recommend putting in a few points- enough to get a comfortable duration- and then letting +skills take care of the rest. With a decent shield, you should be able to achieve max block without a heavy dex investment.
Now, this advice changes if you're trying for a huge defense rating, and pumping HS for that, rather than the blocking (of which you'll already have the lion's share with 10-15 fewer hard skill points spent). For example, some months back, I found a lovely +45 res all etheral paladin shield, and used the bugged socketing recipe on it, and made Exile. This means I have huge defense on the shield, plus Holy Shield, plus Defiance (aura when equipped mod on Exile). As a result, I opted to pump HS, so that blocking is really only an issue when I get hit, which is seldom, even in Hell. Another reason for me pumping HS was because my shield has a fairly low base block (58% for a paladin), and I'm not wearing Guardian Angel (costing me +20% block chance), which means I need that extra block chance, even if it is subject to diminishing returns. If you're instead using a shield like Herald of Zakarum or Stormshield, though, you can achieve max block much easier, which means less points needed here.
As far as Salvation goes, it's well worth a single hard point as a utility aura. If you're careful about gear selection, you really shouldn't need it except when hit by Lower Resist or Conviction (the latter is a non-issue for PvM avengers, though, as your aura will override a boss's). However, it's one of those great party-friendly skills, and if your team is being hammered by elemental attacks, it can really make you popular. If the elemental attacks are all of the same type (gloam lightning bolts, for example), you're better off using the appropriate single-resist aura, as it will give a bigger boost point-for-point, as well as raise the cap on maximum resists (hard points only) for your party members.
Typically, for an avenger, you want a maxed-out Conviction (maxed-out here means slvl 25 after +skills, because the -def% really suffers from diminishing returns here, and the -resist is capped at -150%). This pretty much guarantees you hit things- my avenger (clvl 84) has 1327 AR with Vengeance and all his gear, and has no problems hitting in Hell. I mean, it's like an aura of 'ignore target defense' that works on bosses and players too. It also breaks many immunities and means you do massive damage for targets without immunities. Sorceresses, trapsins, and lightning amazons will adore you, and the Act I merc becomes a powerhouse if you give her a bow with big elemental damage (Harmony is an absolutely incredible choice).
You also want to have anywhere from 5 to 20 hard points in the single resist auras, both to boost your Vengeance damage and to increase your resistance caps. Ten points in each, coupled with Guardian Angel armor, means you have resist caps of 95/95/95/90. Reaching these caps in Hell takes a bit of work, but makes you incredibly durable. You can get by with fewer points if you're set for resists, and/or if you have +max resist from other sources (T-God's Vigor, Guardian Angel, etc). On the other hand, while dumping points here doesn't raise the damage as much as points in Vengeance, it gives you the passive resist cap boost, and it doesn't raise Vengeance's mana cost. Remember than Vengeance doesn't boost the physical damage at all (meaning leeching is hard), and it's very mana-intensive at higher levels compared to other combat skills like Zeal. Slvl 25 Veangeance, easily reachable with max hard points and moderate +skills, costs a whopping 10 mana per swing. I still have only put a single hard point in Vengeance, but if you have big mana leech (Crescent Moon amulet is a great pick), it will do more for your damage if you pump Vengeance instead. Running an Insight merc is another option, as it essentially means you can run Vengeance non-stop without needing leech.
Other utility auras you should grab are Cleansing (mainly for removing curses, but nasty poison such as that from Achmel is easily cured as well) and Redemption (assuming you have no 'slain monsters rest in peace' gear). The latter is especially handy for an avenger; being a single-target attacker, nothing is more discouraging than trying to hack your way through a sea of skeletons, with some unraveler on the other side raising them up as fast as you can cut them down.
