Does it make any difference if I buy altcoins with BTC or ETH??
Honestly, nope. The only difference may be rate parity. Chances are that the dollar value for either exchanges are the same, but you can occasionally find that you'll get a better deal on one or the other for exchanges depending on how each individual coin is performing. An example of this might be as follows:
You want to buy an altcoin called
ABCLet's imagine that
BTC is trading for $10,000
Let's also imagine that
ETH is trading for $1,000
Let's say that
ABC is trading for $50USD per coin
ABC/BTC pairings on the same exchange show that you can buy it with BTC for 0.0048
BTC ($48USD) per ABC
ABC/ETH pairings show that you can buy it for 0.052ETH ($52USD) per ABC
The obvious choice would be to buy the ABC with BTC.
This obviously requires some math, and if this type of stuff interests you, or you have a knack for it, you can even profit from this. You'll occasionally find that this happens because of the volatile nature of cryptocurrencies, and if you're quick enough, you can get into buying for one currency, and immediately trading for another. This is called short trading.
But to answer your question, there is no major difference or drawback of using one currency over another to buy altcoins. It all just depends on the types of pairings that the exchange offers.
