Titles matter. If they didn’t, people wouldn’t have them. However, consider the path beyond that position. You’d maybe be stuck at a senior title level until management but that title could make you more attractive to other employers. Junior titles aren’t as attractive but if you’re in your 20s it probably won’t hurt you.

What really matters is the pay. Senior titles are given out to people in lieu of raises, and in your case they’re offering you a senior title instead of money. Not great. You would also go into that role knowing you’d be stuck there for a while. The junior title implies future growth, and they’re more willing to make an investment in you now.

Think about the future. All things being equal, I’d go for the junior title job.