IMO, (No, not IMHO),
It's hard to beat the Ultimate 1M and SIDE2 combo. You get a FAST PBI hard drive, Multiple OS and BASIC choices (selectable via a BIOS Setup menu), Bluetooth capability (if you have the SIO dongle), Integrated High Speed SIO with any DOS. Real Time Clock, Internal SpartaDOS-X, 1M of RAM, Configurable amount and type of RAM. It even supports CompyShop ANTIC video in banked RAM.
Press the L key on the boot screen, and you have the SIDE Loader. All your .ATR games or whatever can be stored on the FAT32 partition and selected with a menu, or even by joystick.
You can pull your CF drive from your Atari and put it in a Windows machine and drag-n-drop files to/from it.
That's very convenient.
This (and the Incognito [for the original 800]) is/are one of the most important upgrades you can install to bring your Atari into the 21st century and allow you so much flexibility with the system that was un heard of back in the day.
(Well, we had the MARS-8 20 years ago, but that's an entirely different story)
Yes, as you can tell, I a big fan of the U1M & Incognito. I have both.
Antonia is nice, the 816 and lots of Linear RAM open up new worlds of 16 bit possibilities. You can't install both Antonia and U1M,though because they both take over the function of the MMU.
From personal experience, I would stay completely AWAY from the 32-in-1. It is very sensitive to Phi2 timing, and cause problems in 1200XLs and other machines with upgrades. The Multi-OS functionality is included in U1M, Incognito, and Antonia.
U1M and Incognito are flashable from the SDX prompt. Simply type UFLASH and you will have the opportunity to read or write any of the ROM files in the system. You can change any ROM in the system via software. No more pulling EPROMs, erasing, burning, etc.
Read everything you can here, use the search tool to find info about all this stuff.
2017 is a great time to own an Atari! There are so many great products out there, I'm sure you won't be disappointed no matter what you decide upon.
Edit: I forgot to mention that the SIDE2/U1M is MANY,MANY,MANY times faster than any SDRIVE / SIO type solution.
Edited by Kyle22, Fri Feb 17, 2017 10:42 PM.