Officious, intermeddling, but well meaning yank here......
Respectfully SW,
1 if you dont have the technical ability to install or trouble shoot battery power, think carefully about this aspect.
2 the key to using track power (and i have absolutley no preference in this regard) is clean track with clean, tightly fitted rail joiners. Level too. i suggest this track power option as a first foray, respectfully, because it is the most common and is "ready to run ", readily available and, likely, short of the Roundhouse, the best commerical quality.
3 the KEY TO HAPPINESS with model trains, is smooth, trouble free operation. This also appears in the GOod Book, but icannot recall verse and chapter. LOL
4 Ebay is great, provided you know enough to be able to assess what it is youre getting. I agree, choose used items with care. Some considerations, but not all , may be apparent wear to loco wheels and skates, apparent missing parts (very pricey in some cases to locate) , overall cleanliness and box, and , critically, price. Many ebay sellers are not far below discount new locos, at least here in the colonies.
5 i do have a strong bias toward LGB/Marklin, although , they are track powered. For the most part, they are extremely reliable , well engineered, extremely forgiving of knocks (do not underestimate this ) and inclement weather. and will not give you a headache, due to the loco's inherent quality. They can be converted to battery.
6 if you were to ask me, and assuming i nor anyone else would be around to help, or that you might well shun my type, LOL, and be left to yourself, thank you very much, in the confines of the garden , gin and tonic in hand, id suggest that you buy a starter LGB set, passenger or freight, as you fancy. These will be track powered, but can easily be retro fitted battery. The ones with locos with smoke units, i believe, will have a socket on the rear cab of the loco. This can be ideal for a plug in battery system, i believe. I am not, however, able to give you first hand advice in this regard.
I know of no one that has ever regretted having purchased an LGB starter set. Add a bit of track and a structure and some points, and you will have a lot of fun. I certainly loved mine and still do , several decades , and several hundred additions thereto, post acquisition.
I concur, spend a touch more, see it first, and buy from a reliable source. You can then progress to battery.
Best of luck and happiness.