Keep in mind that these are my opinions - other people are welcome to disagree.
Templates
Mage/Weaver/Tamer
110 taming (including your skill increasing items)
115 lore
110 vet
110 mage (wear a tome of lost knowledge for +15 magery to bring yourself to 110)
105 weaving
100+ eval
100 meditation
It is a very powerful template that combines the tanking potential of taming with enough evaluating intelligence and weaving to deal a decent amount of spell damage. In my opinion, once a person learns this template, it is the easiest character to play. Basically, you can invis safely while monsters attack your pet, then cast some cursory spells to help your pet finish the job.
Pros
--Very safe to play, thanks to gift of life, renewal, and attunement
--Easy to keep pets alive, due to gift of renewal, vet, and magery
--Decent amount of damage, due to eval and weaving
Cons
--So easy as to become boring
--Damage output is less than a good archer/tamer's would be
--Without your pet, you basically become a sub-par version of a mage/weaver
Archer/Chiv/Tamer
120 archery
120 tactics
115 lore
110 taming
110 vet
80 chivalry
60 meditation
This is currently one of my all-time favorite tamer templates. This template combines the uber l33t damage output of a chiv/archer with the tanking power of a pet. However, it is much more complicated to play than a mage/weaver/tamer, because in addition to keeping your pet healed via vet and close wounds, you must constantly be tending to your archery, targeting enemies and casting EOO/consecrate weapon. This template, when played right, is the number one top damager in UO, as far as I'm concerned. On the other hand, without invisibility, it is not as safe to play as a mage/weaver.
Pros
--Top damage output
--Very fun to play, keeps you on your toes
--Even without your pet, you can rack up amazing amounts of damage
Cons
--Less safe, without invisibility
--Requires a good suit, which can be difficult/expensive to put together.
Necro/Mage/Tamer
120 Magery
120 Spirit Speak
110 Taming
110 Lore
105 Necro
100 Vet
100 Med
Pros
--The ideal champ spawn template: invis yourself, allow spawn to target your dragon, then wither away
--Animate dead summons do not count as summons, which means you can have a greater dragon and three additional summons
Cons
--You are essentially limited to three offensive spells: Mind Blast (cold damage against a single target), Wither (cold damage, area-of-effect spell), and Poison Strike (poison damage, area-of-effect spell)
Bard/Mage/Tamer
120 Taming
120 Lore
120 Vet
120 Music
120 Discordance (or Peacemaking, or Provocation)
100 Magery
20 [whatever - probably meditation]
Pros
--Discordance + pets = deadly combination. Discordance weakens your enemies. Your pets will be killing your foes before you can say "all kill."
Cons
--Without meditation or evaluating intelligence, you won't be casting any offensive spells.
Archer/Mage/Tamer
120 Archery
110 Tactics
115 lore
110 taming
110 vet
100 magery
50 med
This template is a hybrid of the mage/tamer and the archer/tamer. The benefit is that you can safely invis when in danger and can use archer for damage, instead of spells, to save on mana costs. The downside is that, by being both a mage and an archer, you become slightly less adept at both. You won't have much mana for your mage spells, so you'll need a lot of mana increasing items (40 lower mana cost, too, is a requisite on any suit, including this one). Because your bows have to be spellchanneling, it may prove challenging/expensive to find a good bow.
Suits
For a mage/weaver/tamer, the ideal suit will have:
100 lrc
40 lmc
9+ mana regen
4/6 faster casting/faster cast recovery
Resists in the 60s
For an archer/chiv/tamer, the idea suit will have:
40 lmc
6+ mana regen
4/6 fc/fcr (this requires wearing an orny, a 1/3 ring, and using bows with +1 fc)
Enough stamina increase to bring you to 145+ stamina (for swing speed)
Resists in the 60s
For a necro/mage/tamer, the ideal suit will have:
100 lrc
40 lmc
6+ mr
2/6
+15 or +20 magery for mage weapon
45 dci
Resists in the 60s
For an archer/mage/tamer, the idea suit will have:
100 lrc
40 lmc
9+ mr
2/6
Resists in the 60s
As much stamina and mana increasing items as possible, as you'll be heavily reliant on both.
Example Suit: Fallon Valor (mage/weaver/tamer)
Artifacts - Kasa of the Ra-jin, Pendant of the Magi, Rune Beetle Carapace, Stitcher's Mittens, Tome of Lost Knowledge, Quiver of Infinity, Chaos Vesper Replica Shield, Ornament of the Magician, Shroud of the Condemned, Crimson Cincture, Birds of Britania
Runic/Imbued Items - Arms, legs
Jewelry - Ring with taming, 1 faster casting, and 1 faster cast recovery
Example Suit: Sha'ettemu (necro/mage/tamer)
Artifacts - Mark of Travesty with Spirit Speak and Necromancy, Birds of Britannia, Rune Beetle Carapace, Stitcher's Mittens, Orny, Arcane Shield, Quiver of Infinity, Conjurer's Garb
Runic/Imbued Items - Neck, arms, legs; -20 mage weapon
Jewelry - Ring with 15 magery, 15 taming, 3 faster cast recovery, 15 defense chance increase