Research what others are using in your area. Settling on a digital mode that quickly may lead to disappointment if it's getting little use in your area. While the radio will do analog, don't be too quick to buy into the brand/mode thing just yet.
Be cautious about talking to specific amateurs or clubs, as they will almost always try to steer you towards whatever digital mode they have personally chosen. Take a look at what repeaters are around you, and do some monitoring if you have a scanner. Listen around drive time, in the AM and PM and see where the action is.
As for the portable versus base versus mobile…
Portables are nice, but the low power can hold you back. Adding an external antenna is an option, but that gets old. Using a speaker mic can help a bit, but it makes for inconvenient use.
A base is nice, but only if you do all your operating from home. A good mobile radio with a 12 volt power supply and a good base antenna can work well.
Mobile is a good option if you are commuting or spend a lot of time in your vehicle.
I remember trying to pick my first radio. I went for a dual band hand held. I tried to get on a few nets, but I had trouble getting into repeaters. That created some frustration. I added a base antenna, and that helped. Second purchase was a mobile in my truck, which got a lot of use.
Dual band is nice, but again, take a look at what's used in your area. The dual band was nice for me, but in the end I really ended up only using the VHF side. The mobile I purchased was VHF only.
And remember, it's all about the antenna.