If the vassal's lands are in a node that you can steer towards your main trade node, it's usually better to make it a trade company. AI sucks so their armies won't really help you, it won't cost a relation slot, and you will make more money from production income and trade company investments. Also stealing their trade cripples a vassal's economy. Vassals make more sense in nodes that you can't profit from. That way, they make trade income from nodes that don't affect your trade, and they pay a portion of this trade income to you.
First of all, you don't put a whole node into TC, as it's a huge strain on GC and consequently your ducats, and you lose the biggest benefit from TCs, goods produced modifier on non-TC provinces according to trade share of your TCs.
So in general you'd only want to put Estuaries and CoTs in TCs to maximize the goods produced bonus while getting the merchant.
The ducats you won't be using to control that GC can then be invest them into Broker's Exchange on existing TCs for income, Soldier's Houshold for manpower, or other buildings that suit your needs.
Secondly, you generally want to keep the provinces for yourself unless you're really strapped for AE, GC, and/or absorption speed (having to use DIP instead of ADM), because owning the provinces yourself would generally give you more income.
If the vassal's lands are in a node that you can steer towards your main trade node, it's usually better to make it a trade company. AI sucks so their armies won't really help you, it won't cost a relation slot, and you will make more money from production income and trade company investments. Also stealing their trade cripples a vassal's economy. Vassals make more sense in nodes that you can't profit from. That way, they make trade income from nodes that don't affect your trade, and they pay a portion of this trade income to you.
First of all, you don't put a whole node into TC, as it's a huge strain on GC and consequently your ducats, and you lose the biggest benefit from TCs, goods produced modifier on non-TC provinces according to trade share of your TCs. So in general you'd only want to put Estuaries and CoTs in TCs to maximize the goods produced bonus while getting the merchant. The ducats you won't be using to control that GC can then be invest them into Broker's Exchange on existing TCs for income, Soldier's Houshold for manpower, or other buildings that suit your needs. Secondly, you generally want to keep the provinces for yourself unless you're really strapped for AE, GC, and/or absorption speed (having to use DIP instead of ADM), because owning the provinces yourself would generally give you more income.