The power of the cartridge has nothing to do with what type of bullet to use in a lever gun. When each cartridge gets stripped out of the magazine, the magazine spring slams the rest of the column of cartridges backwards fast and hard. That is a when there is a danger of a pointed bullet firing the primer in the cartridge ahead of it.
Yes, always use flat nosed bullets in a lever gun with a tube feed. Take another look at the bullets in the photo of the cartridges I posted. In addition to Round Nosed Flat Point bullets, the Truncated Cone bullet works well on lever guns. Avoid anything with a sharp shoulder such as a Semi-Wadcutter.
I don't have anything to add as to which rifle to purchase, it has been well covered already. You asked if it was better to save up for the Winchester and I would like to suggest you keep the guns you are thinking of selling and save up the entire amount needed for the gun you want. I did the same thing a few years back, sold some guns I lost interest in and wasn't shooting, to purchase one I just had to have. I now regret selling those guns and to replace them will cost far more than I paid when I bought them. Instant gratification loses it luster quite quickly.