Tactical or Attack Bombers?

Well, if you can't decide, then upgrade both!

depends on doctrine as well as what the enemy is spamming.

I personally go with tact if I'm too lazy to calculate

it depends what your attacking really, tactical bombers are best used against infantry, attack bombers are best for armoured targets

Also consider that attack bombers start with a shorter range. By increasing the attack bomber level, you can achieve a parity of range between the two and keep them grouped easier as well as reduce your need for as many air strips to move your bombers from point A to point B

Sometimes logistical simplicity is worth something.

Plus I find a lot of players like to rely on tanks in the late game. Giving some preference to them is easy to justify.

They work great in a mix, you don't have to think too much what exactly you're attacking, you can just blow away both infantry and armor.

Taking out light armor can be done pretty well with both, but heavy armor is really hard with tacs and infantry is a really bad target for AB's. When your enemy has tank-only stacks even tacs can take them out because tanks have REALLY bad AA values, it just takes a bit longer. Attacking infantry with just AB's is a real no-go though.

If you're using the allies doctrine, you can usually get away with spamming tac bombers. The limited range on the attack bombers is a real handicap.

Axis attack bombers are extremely effective, really depends off of what your enemy uses. If they rely off of tanks then go attack if they spam infantry use tacts.